Flexible, modular, compact fiber switch improvements

ABSTRACT

A fiber optic switch ( 400 ) includes a fiber optic switching module ( 100 ) that receives and fixes ends ( 104 ) of optical fibers ( 106 ). The module ( 100 ) includes numerous reflective light beam deflectors ( 172 ) arranged in a V-shape which may be selected as pairs for coupling a beam of light ( 108 ) between a pair of optical fibers ( 106 ). The module ( 100 ) also produces orientation signals from each deflector ( 172 ) which indicate its orientation. A portcard ( 406 ) supplies drive signals to the module ( 100 ) for orienting at least one deflector ( 172 ). The portcard ( 406 ) also receives the orientation signals produced by that deflector ( 172 ) together with coordinates that specify an orientation for the deflector ( 172 ). The portcard ( 406 ) compares the received coordinates with the orientation signals and adjusts the drive signals supplied to the module ( 100 ) to reduce any difference between the received coordinates and the orientation signals. The switch ( 400 ) also employs optical alignment to precisely orient pairs deflectors ( 172 ) coupling a beam of light ( 108 ) between optical fibers ( 106 ).

This application claims the benefit of provisional application Ser. No.60/144,953 filed Jul. 21, 1999.

TECHNICAL FIELD

The present invention relates generally to the technical field of fiberoptics, and, more particularly, to free-space, reflective N×N fiberoptic switches.

BACKGROUND ART

A dramatic increase in telecommunications during recent ears, which maybe attributed largely to increasing Internet communications, hasrequired rapid introduction and commercial adoption of innovations infiber optic telephonic communication systems. For example, recentlyfiber optic telecommunication systems have been introduced and are beinginstalled for transmitting digital telecommunications concurrently on 4,16, 32, 64 or 128 different wavelengths of light that propagate along asingle optical fiber. While multi-wavelength fiber optictelecommunications dramatically increases the bandwidth of a singleoptical fiber, that bandwidth increase is available only at both ends ofthe optical fiber, e.g. between two cities. When light transmitted intoone end of the optical fiber arrives at the other end of the opticalfiber, there presently does not exist a flexible, modular, compact, N×Nfiber optic switch which permits automatically forwarding light receivedat one end of the optical fiber onto a selected one of several differentoptical fibers which will carry the light onto yet other destinations.

Historically, when telecommunications were transmitted by electricalsignals via pairs copper wires, at one time a human being called atelephone operator sat at a manually operated switchboard and physicallyconnected an incoming telephone call, received on one pair of copperwires, that were attached to a plug, to another pair of copper wires,that were attached to a socket, to complete the telephone circuit. Thetelephone operator's task of manually interconnecting pairs of wiresfrom two (2) telephones to establish the telephone circuit was firstreplaced by an electro-mechanical device, called a crossbar switch,which automated the operator's manual task in response to telephonedialing signals. During the past forty years, the electro-mechanicalcrossbar switch for electrical telecommunications has been replaced byelectronic switching systems.

Presently, switches for fiber optic telephonic communications existwhich perform functions for fiber optic telephonic communicationsanalogous to or the same as the crossbar switch and electronic switchingsystems perform for electrical telephonic communications. However, thepresently available fiber optic switches are far from ideal. That is,existing fiber optic telecommunications technology lacks a switch thatperforms the same function for optical telecommunications as thatperformed by electronic switching systems for large numbers of opticalfibers.

One approach used in providing a 256×256 switch for fiber optictelecommunications first converts light received from a incoming opticalfiber into an electrical signal, then transmits the electrical signalthrough an electronic switching network. The output signal from thatelectronic switching network is then used to generate a second beam oflight that then passes into an output optical fiber. As those familiarwith electronics and optical fiber telecommunications recognize, thepreceding approach for providing a 256×256 fiber optic switch isphysically very large, requires electrical circuits which processextremely high-speed electronic signals, and is very expensive.

Attempting to avoid complex electronic circuits and conversions betweenlight and electronic signals, various proposals exist for assembling afiber optic switch that directly couples a beam of light from oneoptical fiber into another optical fiber. One early attempt to provide afiber optic switch, analogous to the electrical crossbar switch, mimicswith machinery the actions of a telephone operator only with opticalfibers rather than for pairs of copper wires. U.S. Pat. No. 4,886,335entitled “Optical Fiber Switch System” that issued Dec. 12, 1989,includes a conveyor that moves ferrules attached to ends of opticalfibers. The conveyer moves the ferrule to a selected adapter and plugsthe ferrule into a coupler/decoupler included in the adapter. After theferrule is plugged into the coupler/decoupler, light passes between theoptical fiber carried in the ferrule and an optical fiber secured in theadapter.

U.S. Pat. No. 5,864,463 entitled “Miniature 1×N ElectromechanicalOptical Switch And Variable Attenuator” which issued Jan. 26, 1999,(“the '463 patent”) describes another mechanical system for selectivelycoupling light between one optical fiber and one of a number of opticalfibers. This patent discloses selectively coupling light between oneoptical fiber and a selected optical fiber by mechanically moving an endof one optical fiber along a linear array of ends of the other opticalfibers. The 1×N switch uses a mechanical actuator to coarsely align theend of the one optical fiber to a selected one of the other opticalfibers within 10 μm. The 1×N switch, using light reflected back into themoving optical fiber from the immediately adjacent end of the selectedoptical fiber, then more precisely aligns the end of the input opticalfiber to the output optical fiber. U.S. Pat. No. 5,699,463 entitled“Mechanical Fiber Optic Switch” that issued Dec. 16, 1997, also alignsan end of one optical fiber to one of several other optical fibersassembled as a linear array, but interposes a lens between ends of thetwo optical fibers.

U.S. Pat. No. 5,524,153 entitled “Optical Fiber Switching System AndMethod Of Using Same” that issued Jun. 4, 1996, (“the '153 patent”)disposes two (2) optically opposed groups of optical fiber switchingunits adjacent to each other. Each switching unit is capable of aligningany one of its optical fibers with any one of the optical fibers of theoptically opposed group of switching units. Within the switching unit,an end of each optical fiber is positioned adjacent to a beamforminglens, and is received by a two-axis piezoelectric bender. The two-axispiezoelectric bender is capable of bending the fiber so light emittedfrom the fiber points at a specific optical fiber in the opticallyopposed group of switching units. Pulsed light generated by radiationemitting devices (“REDs”) associated with each optical fiber pass fromthe fiber to the selected optical fiber in the opposing group. Thepulsed light from the RED received by the selected optical fiber in theopposing group is processed to provide a signal that is fed back to thepiezoelectric bender for pointing light from the optical fiber directlyat the selected optical fiber.

Rather than mechanically effecting alignment of a beam of light from oneoptical fiber to another optical fiber either by translating or bybending one or both optical fibers, optical switches have been proposedthat employ micromachined moving mirror arrays to selectively couplelight emitted from an input optical fiber to an output optical fiber.Papers presented at OFC/IOOC '99, Feb. 21-26, 1999, describe elementsthat could be used to fabricate s a three (3) stage fully non-blockingfiber optic switch, depicted graphically in FIG. 1. This fiber opticswitch employs moving mirror arrays in which each polysilicon mirror canselectively reflect light at a 90° angle. In this proposed fiber opticswitch, rows of relatively small 32×64 optical switching arrays 52 a_(i) (i=1, 2 . . . 32) and 52 b _(k) (k=1, 2 . . . 32) receive lightfrom or transmit light to thirty-two (32) input or output optical fibers54 a _(n) and 54 b _(n). Thirty-two groups of sixty-four (64) opticalfibers 56 a _(l,m) and 56 b _(l,m) carry light between each of the 32×64optical switching arrays 52 a _(i) and 52 b _(k) and one of sixty-four32×32 optical switching arrays 58 _(j) (j=1, 2 . . . 64).

The complexity of the fiber optic switch illustrated in FIG. 1 isreadily apparent. For example, a 1024×1024 fiber optic switch assembledin accordance with that proposal requires 4096 individual optical fibersfor interconnecting between the 32×64 optical switching arrays 52 a _(i)and 52 b _(k) and the 32×32 optical switching arrays 58 _(j). Moreover,the 32×64 optical switching arrays 52 a _(i) and 52 b _(k) and 32×32optical switching arrays 58 _(j) require a total of 196,608micromachined mirrors.

The polysilicon mirrors proposed for the fiber optic switch illustratedin FIG. 1 are curved rather than optically flat. Furthermore, whilethose mirrors possess adequate thermal dissipation for switching asingle 0.3 mW wavelength of light and perhaps even a few suchwavelengths, they are incapable of switching even ten (10) or twenty(20) such wavelengths. However, as described above fiber optictelecommunications systems are already transmitting many more thantwenty (20) wavelengths over a single optical fiber, and, if notalready, will soon be transmitting hundreds of wavelengths. If insteadof a single wavelength of light one optical fiber carries 300 differentwavelengths of light each having a power of 0.3 mW, then 100 mW of powerimpinges upon the polysilicon mirror proposed for this fiber opticswitch. If the polysilicon mirror reflects 98.5% of that light, themirror must absorb substantially all of the remainder, i.e. 1.5 mW ofpower. Absorption of 1.5 mW of power would likely heat the thermallynon-conductive polysilicon mirror to unacceptable temperatures whichwould further degrade mirror flatness.

U.S. Pat. No. 4,365,863 entitled “Optical Switch For a Very Large Numberof Channels” that issued Dec. 28, 1982, (“the '863 patent”) disclosesdisposing two (2) parallel arrays of optically opposed, regularly placedends of optical fibers. The space between the two (2) arrays contains anoptical switching system that includes propagation mode converters thatare associated respectively with each fiber of each array. The modeconverters convert light from the guided mode of propagation in glassfilaments to a directive mode of propagation in free space, andvice-versa. In its simplest form, such a converter comprises essentiallyan optical lens whose focal point is positioned approximately at the endof the corresponding fiber.

The optical switching system of the '863 patent also includes a lightbeam deflector associated with each fiber of its two arrays. Any modeconverter of one array sends a beam of light to a deflector with whichit is associated. The deflector receiving the light beam from the modeconverter redirects the light to any one of the deflectors associatedwith the other array of optical fibers. The deflector receiving the beamfrom a deflector redirects the light to the mode converter associatedwith the receiving light deflector. The light beam deflectors may be ofany known type. The '863 patent specifically discloses using for lightbeam deflectors either a mechanical-optical device that operates on theprinciple of the diasporameter, or an acousto-optical deflectors basedon photon-phonon interaction within a crystal medium.

Each light beam deflector in the '863 patent is controlled by aninterface control that is driven by a logic circuit. A detector isassociated with each beam of light to extract from the signal carried bythe beam the data corresponding to the address of the optical fiber inthe respective arrays. The logic circuits are connected to a centralprocessor which, together with these logic circuits, controls all thefunctions of the switching system. Each detector in the '863 patent may,for example, include a semi-transparent mirror sampling thecorresponding beam of light, an optoelectronic device for converting thesample of the beam of light into an electrical signal, and a device fordecoding this electrical signal in order to extract the optical fiberaddress data.

A technical paper entitled “A Silicon Light Modulator” by KariGustafsson and Bertil Hök published in the Journal of Physics E.Scientific Instruments 21 at pages 680-85 (“the Gustafsson, et al.paper) describes an array of four, one-dimensional torsional scannersmicromachined from an epitaxial layer of a silicon substrate. TheGustafsson, et al. paper describes electrostatically exciting thetorsional scanners. The paper reports that operating in this way thetorsional scanners have been used in a fiber-optic switch and modulatorto couple light between a pair of immediately adjacent optical fibers.

DISCLOSURE OF INVENTION

The present invention provides a fiber optic switch capable ofconcurrently coupling incoming beams of light carried on more than 1,000individual optical fibers to more than 1,000 outgoing optical fibers.

An object of the present invention is to provide a simpler fiber opticswitch that is capable of switching among a large number of incoming andoutgoing beams of light carried on optical fibers.

Another object of the present invention is to provide an efficient fiberoptic switch that is capable of switching among a large number ofincoming and outgoing beams of light carried on optical fibers.

Another object of the present invention is to provide a fiber opticswitch which has low cross-talk between communication channels.

Another object of the present invention is to provide a fiber opticswitch which has low cross-talk between communication channels duringswitching thereof.

Another object of the present invention is to provide an highly reliablefiber optic switch.

Another object of the present invention is to provide a fiber opticswitch that does not exhibit dispersion.

Another object of the present invention is to provide a fiber opticswitch that is not polarization dependent.

Another object of the present invention is to provide a fiber opticswitch that is fully transparent.

Another object of the present invention is to provide a fiber opticswitch that does not limit the bitrate of fiber optic telecommunicationspassing through the switch.

Briefly, the present invention is a fiber optic switching module adaptedfor use in a fiber optic switch that includes a first and a second groupof optical fiber receptacles. The two groups of optical fiberreceptacles are separated from each other at opposite ends of a freespace optical path. Each optical fiber receptacle is adapted forreceiving and fixing an end of an optical fiber. The fiber opticswitching module also includes lenses one of which is fixed respectivelyat each of the optical fiber receptacles of the first and second groupsso the end of the optical fiber fixable in that optical fiber receptacleis juxtaposed with the lens fixed thereat. Each lens is adapted forreceiving a beam of light emittable from the juxtaposed end of theoptical fiber and for emitting a quasi-collimated beam of light into theoptical path of the fiber optic switching module.

The fiber optic switching module also includes a first and a second setof reflective light beam deflectors that are disposed in a V-shapedarrangement within the optical path between the groups of optical fiberreceptacles. Each of the light beam deflectors respectively is:

1. associated with one of the lenses fixed at each of the optical fiberreceptacles;

2. located so the quasi-collimated beam of light emittable from theassociated lens impinges upon the light beam deflector to be reflectedtherefrom; and

3. energizable by drive signals supplied to the fiber optic switchingmodule to be oriented for reflecting the quasi-collimated beam of lightemittable from the associated lens to also reflect off a selected lightbeam deflector.

Also included in the fiber optic switching module is a mirror disposedalong the optical path between the sets of light beam deflectors uponwhich quasi-collimated beams of light impinge.

Arranged in this way, a pair of light beam deflectors may be selectedand oriented by the drive signals supplied thereto to establish anoptical coupling for at least one quasi-collimated beam of light betweena pair of lenses respectively fixable at any one of the optical fiberreceptacles and another lens fixable at any other of the optical fiberreceptacles.

These and other features, objects and advantages will be understood orapparent to those of ordinary skill in the art from the followingdetailed description of the preferred embodiment as illustrated in thevarious drawing figures.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a proposed, prior art three (3)stage fully non-blocking fiber optic switch;

FIG. 2 is a plan view ray tracing diagram illustrating propagation oflight beams through a trapezoidally-shaped free space, convergent beamN×N reflective switching module in accordance with the presentinvention;

FIG. 3 is a plan or elevational schematic diagram illustrating a singlebeam of light as may propagate between sides A and B of thetrapezoidally-shaped free space, convergent beam N×N reflectiveswitching module depicted in FIG. 2 in accordance with the presentinvention;

FIG. 4a is a perspective view ray tracing diagram illustratingpropagation of light beams through an alternative embodiment,rectangularly-shaped free space, convergent beam N×N reflectiveswitching module in accordance with the present invention;

FIG. 4b is plan view ray tracing diagram illustrating propagation ofconvergent light beams through the rectangularly-shaped reflectiveswitching module illustrated in FIG. 4a in accordance with the presentinvention;

FIG. 5 is a plan view ray tracing diagram illustrating propagation oflight beams through an alternative embodiment, polygonally-shaped freespace, convergent beam N×N reflective switching module in accordancewith the present invention;

FIG. 6 is a plan view ray tracing diagram illustrating propagation oflight beams through a trapezoidally-shaped free space, convergent beamreflective switching module in accordance with the present inventionthat permits coupling a beam of light between any arbitrarily chosenpair of optical fibers;

FIG. 6a is a plan view ray tracing diagram illustrating free spacepropagation of light beams through a convergent beam reflectiveswitching module in accordance with the present invention that has aV-shaped array of light beam deflectors, and that, similar to theswitching module of FIG. 6, permits coupling a beam of light between anyarbitrarily chosen pair of optical fibers;

FIG. 7 is a plan view ray tracing diagram illustrating propagation oflight beams through an alternative trapezoidally-shaped free space,convergent beam N×N reflective switching module in accordance with thepresent invention which is more compact than the N×N reflectiveswitching module depicted in FIG. 5;

FIG. 8a is an elevational view illustrating a preferred, cylindricallyshaped micro-lens adapted for use in the N×N reflective switchingmodule;

FIG. 8b is an elevational view illustrating a micro-lens adapted for usein the N×N reflective switching module that permits closer spacingbetween lenses and fibers;

FIG. 9 is a partially cross-sectioned elevational view illustrating aconvergence block included both in the side A and in side B of the N×Nreflective switching module depicted in FIG. 7 that receives taperedoptical fiber collimator assemblies;

FIG. 10 is a partially cross-sectioned plan view illustrating theconvergence block depicted in FIG. 9 that receives tapered optical fibercollimator assemblies;

FIG. 10a is a partially cross-sectioned plan view illustrating analternative convergence block that permits adjusting the position andorientation of the lenses;

FIG. 10b is a cross-sectioned elevational view illustrating of thealternative convergence block taken along the line 10 a—10 a of FIG.10a;

FIG. 11 is a partially cross-sectioned elevational view illustrating amicro-lens adapted for use in the N×N reflective switching module forconcurrently switching light carried by a duplex pair of optical fibers;

FIG. 12 is an elevational view illustrating a preferred type of siliconwafer substrate used in fabricating torsional scanners;

FIG. 13 is a plan view illustrating a 2D electrostatically energizedtorsional scanner particularly adapted for use in reflective switchingmodules such as those illustrated in FIGS. 2, 4 a-4 b, 5, 6, 6 a and 7;

FIG. 14a is an enlarged plan view illustrating a torsional flexure hingeused in the torsional scanner taken along the line 14 a—14 a in FIG. 13;

FIG. 14b is an enlarged plan view illustrating a slotted torsion-barhinge used in the torsional scanner taken along the line 14 b—14 b inFIG. 13;

FIG. 15 is a schematic cross-sectional elevational view illustrating atorsional scanner disposed above an insulating substrate havingelectrodes deposited thereon with a beam of light reflecting off amirror surface located on the backside of a device layer;

FIGS. 15a and 15 b are alternative plan views of the electrodes and aportion of the insulating substrate taken along the line 15 a/15 b—15a/15 b in FIG. 15.

FIG. 16a is an elevational view illustrating a strip of torsionalscanners adapted for use in reflective switching modules such as thoseillustrated in FIGS. 2, 4 a-4 b, 5, 6, 6 a and 7;

FIG. 16b is a cross-sectional plan view taken along the line 16 b—16 bin FIG. 16a illustrating overlapping immediately adjacent strips oftorsional scanners to reduce the horizontal distance between immediatelyadjacent strips;

FIG. 16c is an elevational view illustrating a preferred strip oftorsional scanners adapted for use in reflective switching modules suchas those illustrated in FIGS. 2, 4 a-4 b, 5, 6, 6 a and 7;

FIG. 16d is a cross-sectional plan view illustrating the preferred stripof torsional scanners taken along the line 16 d—16 d in FIG. 16c;

FIG. 16e is across-sectional plan view taken along the line 16 d—16 d inFIG. 16a illustrating juxtaposition of the strips of torsional scannersdepicted in FIG. 16c;

FIG. 17a is a plan view illustrating vertically offset strips oftorsional scanners which permits a denser arrangement of optical fibersin reflective switching modules such as those illustrated in FIGS. 2, 4a-4 b, 5, 6, 6 a and 7;

FIG. 17b is a plan view illustrating an even denser packing of offsetrows or columns of torsional scanners that may be employed if all thetorsional scanners are fabricated as a single monolithic array ratherthan in strips;

FIG. 18a is a plan view illustrating an alternative embodiment of thetorsional scanner in which the outer torsional flexure hinges areoriented diagonally with respect to the scanner's outer frame;

FIG. 18b is a plan view illustrating an array of torsional scanner ofthe type illustrated in FIG. 18a;

FIG. 19a is a plan view illustrating an alternative embodiment of thetorsional scanner in which the inner torsional flexure hinges areoriented along a diagonal of the scanner's non-square mirror plate;

FIG. 19b is a plan view illustrating an alternative embodiment of thetorsional scanner depicted in FIG. 19a in which both pairs of torsionalflexure hinges are suitably oriented with respect to crystallographicdirections of silicon to permit fabrication of torsion sensors thereinthat have optimum characteristics;

FIG. 20a is an elevational view illustrating a dense arrangement of thetorsional scanner illustrated in FIG. 18a adapted for inclusion inreflective switching modules such as those illustrated in FIGS. 2, 4 a-4b, 5, 6, 6 a and 7;

FIG. 20b is an elevational view illustrating a dense arrangement of thetorsional scanner illustrated in FIG. 19a adapted for inclusion inreflective switching modules such as those illustrated in FIGS. 2, 4 a-4b, 5, 6, 6 a and 7;

FIG. 21 is a schematic cross-sectional elevational view illustrating analternative embodiment strip of torsional scanners fastened to asubstrate which also carries a mirror strip thereby permitting anarrangement in which collimator lenses and ends of optical fibers arepositioned close to mirror surfaces on the torsional scanners;

FIG. 21a is a schematic elevational view illustrating arranging stripsof torsional scanners illustrated in FIG. 21 to provide one dimensionalconvergence;

FIG. 21b is a schematic elevational view illustrating arranging opticalfiber collimator assemblies to provide one dimensional convergence forcombination with the one dimensional convergence of torsional scannersillustrated in FIG. 21a;

FIG. 22a is a front elevational view of a strip of torsional scannersflip-chip bonded to a substrate;

FIG. 22b is a cross-sectioned, side elevational view of the strip oftorsional scanners flip-chip bonded to the substrate taken along theline 22 b—22 b in FIG. 22a;

FIG. 22c is a top view of the strip of torsional scanners that isflip-chip bonded to the substrate taken along the line 22 c—22 c in FIG.22a;

FIG. 22d is a cross-sectioned, side elevational view of the strip oftorsional scanners flip-chip bonded to a silicon substrate having viasformed therethrough;

FIG. 22e is a cross-sectioned, side elevational view of a portion of asurface of the torsional scanner having troughs formed therein tostrengthen the bond to the substrate;

FIG. 22f is a cross-sectioned, side elevational view similar to that ofFIG. 22b showing a spacer interposed between the strip of torsionalscanners and the substrate;

FIG. 23 is a ray tracing diagram illustrating scattering of light fromportions of a torsional scanner that surrounds the mirror surfacethereof;

FIG. 24 is a system level block diagram illustrating reflectiveswitching modules such as those illustrated in FIGS. 2, 4 a-4 b, 5, 6, 6a and 7;

FIG. 25 is a perspective drawing illustrating a modular fiber opticswitch in accordance with the present invention;

FIG. 26 is a overall block diagram for modular fiber optic switchdepicted in FIG. 25 including a portcard and the reflective switchingmodule;

FIG. 26a is a diagram illustrating one embodiment of photodetectors thatmay be used in an optical alignment servo for precisely orienting a pairof mirrors included in the reflective switching module;

FIG. 26b is a diagram illustrating a compound photo-detector that may beused in an optical alignment servo for precisely orienting a pair ofmirrors included in the reflective switching module;

FIG. 26c is a diagram schematically illustrating how bent-fiber taps maybe used on portcards to extract light from an optical fiber foralignment and other diagnostic purposes;

FIG. 26d is an elevational view of a bent-fiber tap taken along the line26 d—26 d in FIG. 26c;

FIG. 27a is a block diagram illustrating a servo system which ensuresprecise alignment of mirrors included in a reflective switching moduleincluded in the modular fiber optic switch depicted in FIG. 25, such asone of the reflective switching modules illustrated in FIGS. 2, 4 a-4 b,5, 6, 6 a and 7;

FIG. 27b is a block diagram illustrating one channel, either x-axis ory-axis, of a dual axis servo included in the servo system depicted inFIG. 27a;

FIG. 27c is a block diagram illustrating sharing a single channel of onedual axis servo among several different pairs of torsional scannerelectrodes 214;

FIG. 27d is a block diagram illustrating a circuit for inducingcontrolled rotation of a torsional scanner using alternating current(“AC”) driving voltages;

FIGS. 27e and 27 f are waveform diagrams illustrating voltages appliedbetween electrodes and the mirror plate of the torsional scanner;

FIG. 28a is a partially cross-sectioned elevational view illustrating analternative embodiment double plate structure for receiving and fixingan array of optical fibers;

FIG. 28b is an elevational view illustrating a profile for one type ofhole that may be formed through one of the plates taken along the line28 b—28 b in FIG. 28a;

FIG. 28c is an elevational view illustrating an array of XY micro-stagesformed in one of the plates taken along the line 28 c—28 c in FIG. 28a;

FIG. 29a is an elevational view illustrating an XY micro-stage of a typeincluded array taken along the line 29 a-298 in FIG. 28c;

FIGS. 29b and 29 c are elevational views illustrating a portion ofalternative embodiment XY micro-stages taken along the line 29 b/29 c—29b/29 c in FIG. 29a;

FIG. 30a is a partially cross-sectioned view illustrating a lensmicromachined from a silicon substrate that can be electrostaticallyactivated to move along the lens' longitudinal axis;

FIG. 30b is an elevational view illustrating the silicon micromachinedlens taken along the line 30 b—30 b in FIG. 30a;

FIG. 30c is a partially cross-sectioned view illustrating a lensmicromachined from a silicon substrate, similar to the lens illustratedin FIG. 30a, that can be electro-magnetically activated to move alongthe lens' longitudinal axis;

FIG. 31a is a plan view illustrating one configuration for usingmagnetic force in effecting rotation of torsional scanners;

FIG. 31b is an elevational view of a magnet used therein taken along theline 31 b—31 b in FIG. 31a;

FIG. 31c is a plan view illustrating another configuration for usingmagnetic force in effecting rotation of torsional scanners;

FIG. 31d is an elevational view of a magnet used therein taken along theline 31 d—31 d in FIG. 31c;

FIG. 32 is an elevational view that illustrates coupling beams of lightfrom a routing wavelength demultiplexer directly into one of thereflective switching modules illustrated in FIGS. 2, 4 a-4 b, 5, 6, 6 aand 7;

FIGS. 33a and 33 b are respectively schematic diagrams illustrating aLittrow cavity formed by a grating formed on a 2D torsional scannertogether with a laser-diode, and as applied for wavelength conversionthat can be advantageously applied in telecommunication; and

FIG. 34, is a schematic diagram illustrating using a torsional scannercarrying a grating for monitoring wavelengths of light that propagatealong an optical fiber.

BEST MODE FOR CARRYING OUT THE INVENTION

Free space,

Convergent Beam,

Double Bounce,

Reflective Switching Module

FIG. 2 depicts ray tracings for light beams propagating through atrapezoidally-shaped, convergent beam, double bounce N×N reflectiveswitching module in accordance with the present invention that isreferred to by the general reference character 100. The N×N reflectiveswitching module 100 includes sides 102 a and 102 b which are spacedapart from each other at opposite ends of a C-shaped free space opticalpath. Although as described below other geometrical relationships forthe sides 102 a and 102 b may occur for other configurations of the N×Nreflective switching module 100, for the embodiment of the N×Nreflective switching module 100 illustrated in FIG. 2 having theC-shaped free space optical path the sides 102 a and 102 b arepreferably coplanar. Both side 102 a and side 102 b are adapted toreceive and fix ends 104 of N optical fibers 106, for exampleone-thousand one-hundred fifty-two (1152) optical fibers 106. The Noptical fibers 106 are arranged in a rectangular array with thirty-six(36) columns, each of which contains thirty-two (32) optical fibers 106.A lens 112 is disposed immediately adjacent to the ends 104 of each ofthe optical fibers 106 along the optical path between sides 102 a and102 b. Each of the lenses 112 are disposed with respect to the end 104of the optical fiber 106 with which it is associated to produce fromlight, which may be emitted from the end 104 of the associated opticalfiber 106, a quasi-collimated beam that propagates along the opticalpath between sides 102 a and 102 b.

FIG. 3 graphically illustrates a single beam of light 108 from a singleoptical fiber 106 as may propagate between sides 102 a and 102 b, orconversely. For wavelengths of light conventionally used in single modefiber optic telecommunications, the lens 112 is a micro-lens whichtypically has a focal length of 2.0 to 12.0 mm. Such a lens 112 producesa quasi-collimated beam preferably having a diameter of approximately1.5 mm which propagates along a five-hundred (500) to nine-hundred (900)mm long path between the sides 102 a and 102 b. Since the N×N reflectiveswitching module 100 preferably uses the maximum relay length of thelens 112, the end 104 of each optical fiber 106 is positioned at thefocal length of the lens 112 plus the Raleigh range of the beam of light108 emitted from the optical fiber 106. Consequently, if the end 104 ofthe optical fiber 106 is displaced a few microns along the axis of thelens 112, that produces a negligible effect on the direction along whichthe maximum relay length quasi-collimated beam propagates between thesides 102 a and 102 b. Typically the exit angle of the maximum relaylength quasi-collimated beam from the lens 112 will be a fraction of onemilliradian, i.e. 0.001 radian. As will be described in greater detailbelow, any possible misalignment of the maximum relay lengthquasi-collimated beam due to misalignment between the end 104 of theoptical fiber 106 and the lens 112 can be easily accommodated byproviding sufficiently large surfaces from which the beam reflects.

After passing through the associated lens 112, a beam of light 108emitted from the end 104 of each optical fiber 106 reflects first off amirror surface 116 a or 116 b, indicated by dashed lines in FIG. 3, thatis associated with a particular lens 112 and optical fiber 106 pair. Themirror surfaces 116, described in greater detail below, are preferablyprovided by two-dimensional (“2D”) torsional scanners of a type similarto those described in U.S. Pat. No. 5,629,790 (“the '790 patent”), thatis incorporated herein by reference. The N×N reflective switching module100 includes two sets 118 a and 118 b of mirror surfaces 116respectively disposed between the lenses 112 along the optical pathbetween the sides 102 a and 102 b. Each set 118 a or 118 b includes anumber of individual, independent mirror surfaces 116, each of which issupported by a pair of gimbals that permits each mirror surface 116 torotate about two non-parallel axes. The number of mirror surfaces 116equals the number, N, of optical fibers 106 and lenses 112 at thenearest side 102 a or 102 b. After reflecting off the mirror surface 116a or 116 b, the beam of light 108, propagating between sets 118 a and118 b in FIG. 2, then reflects off a selected one (1) of the mirrorsurface 116 b or 116 a further along the C-shaped optical path betweenthe sides 102 a and 102 b, through one of the lenses 112 at the distantside 102 b or 102 a, and into the optical fiber 106 associated with thatparticular lens 112.

FIGS. 4a-4 b depict ray tracings for light beams propagating through analternative embodiment, rectangularly-shaped, convergent N×N reflectiveswitching module 100. The rectangularly-shaped configuration of the N×Nreflective switching module 100 illustrated in FIGS. 4a-4 b employs ahorizontally-elongated Z-shaped free space optical path. While in theillustration of this FIG. the distances between the side 102 a and thecurved set 118 a, the curved set 118 a and the curved set 118 b, thecurved set 118 b and the side 102 b are substantially equal, thoseskilled in the art will recognize that these distances need not beequal. Moreover, those skilled in the art will recognize that the sets118 a and 118 b may be curved to provide either one dimensional (“1D”)or 2D convergence. Thus, for the configuration of the N×N reflectiveswitching module 100 depicted in FIGS. 4a-4 b the curved set 118 a maybe advantageously moved nearer to the side 102 a and the curved set 118b moved nearer to the side 102 b. Such a shortening of the distancesbetween the sides 102 a and 102 b and the curved sets 118 a and 118 bcorrespondingly lengthens the distance between the curved set 118 a andcurved set 118 b which produces a parallelogram-shaped N×N reflectiveswitching module 100. FIG. 5 depicts ray tracings for light beamspropagating through an alternative embodiment, polygonally-shaped N×Nreflective switching module 100. The polygonally-shaped configuration ofthe N×N reflective switching module 100 illustrated in FIG. 5 alsoproduces a Z-shaped free space optical path.

FIG. 6 depicts a trapezoidally-shaped reflective switching module 100that consist of only one half of the N×N reflective switching module 100depicted in FIG. 1, i.e. either the left half thereof or the right halfthereof. The reflective switching module 100 depicted in FIG. 6fundamentally differs from that depicted in FIG. 1 only by including amirror 120 disposed at the middle of the optical path between sides 102a and 102 b. The mirror 120 should have as high a reflectivity aspossible at the relevant wavelengths of light, with the s and preflectivity balanced, as is well known in the art. While for equivalentsides 102 a the reflective switching module 100 depicted in FIG. 6 cancouple light selectively between only one-half as many optical fibers106 as the N×N reflective switching module 100 illustrated in FIG. 1,the reflective switching module 100 depicted in FIG. 6 can couple lightbetween any arbitrarily chosen pair of those optical fibers 106.

FIG. 6a depicts another type of N×N reflective switching module 100assembled by abutting two, mirror-image reflective switching modules ofthe general type illustrated in FIG. 6. The configuration for thereflective switching module 100 illustrated in FIG. 6 includes sides 102a and 102 b with the sets 118 a and 118 b of mirror surfaces 116arranged to form a V-shape. The arrangement of mirror surfaces 116 andsides 102 a and 102 b illustrated in FIG. 6a has some advantages overthe arrangement depicted in FIG. 6. In comparison with the arrangementdepicted in FIG. 6, the set 118 a and side 102 a are divided into twoparts, i.e. the sides 102 a and 102 b and the sets 118 a and 118 b.Dividing the sides 102 a and 102 b and the sets 118 a and 118 b into twoparts reduces the distance between the sides 102 a and 102 b and theircorresponding sets 118 a and 118 b of mirror surfaces 116 withoutincreasing the deflection angles needed to couple light between any twoarbitrarily chosen optical fibers 106. This arrangement allows buildingreflective switching modules 100 having a larger number of opticalfibers 106 by easing the collimator pointing tolerance.

FIG. 7 depicts another trapezoidally shaped N×N reflective switchingmodule 100 which also employs a mirror 120 for folding the optical pathof the N×N reflective switching module 100 depicted in FIG. 5. Foldingthe optical path into a W-shape provides a more compact reflectiveswitching module 100 than the N×N reflective switching module 100depicted in FIG. 1.

Considering the beam of light 108 depicted schematically in FIG. 3,solely from the perspective of optical design, the various differentembodiments of the reflective switching module 100 described above andillustrated in FIGS. 2, 4 a, 4 b, 5, 6, 6 a, and 7 differ principally inthe location of the mirror surfaces 116 a and 116 b along the beam oflight 108, and in the folding of the optical path. For example, in theembodiment of the N×N reflective switching module 100 illustrated inFIGS. 4a-4 b the mirror surfaces 116 a and 116 b are locatedapproximately one-third (⅓) of the path length between the sides 102 aand 102 b from the nearest lenses 112. Conversely for otherconfigurations of the reflective switching module 100 such as thoseillustrated in FIGS. 2, 5, 6, and 7 the mirror surfaces 116 a and 116 bare immediately adjacent to the respective sides 102 a and 102 b.However, those skilled in the art of optical design will readilyunderstand that differences among the various configurations,particularly locations for the mirror surfaces 116 a and 116 b withrespect to the lenses 112 and the ends 104 of the optical fibers 106,influence or affect other more detailed aspects of the optical design.

Those skilled in the art of optical design will also understand thatconceptually there exist an unlimited number of other possiblegeometrical arrangements and optical path shapes in addition to thoseillustrated in FIGS. 2, 4 a, 4 b, 5, 6 and 7 for placing the ends 104 ofthe optical fibers 106 respectively at one or more the sides 102 a and102 b, the associated lenses 112 and the mirror surfaces 116 a and 116b. With regard to such alternative geometrical arrangements for the freespace optical path of the reflective switching module 100, a preferencefor one arrangements in comparison with other possible arrangementsusually involves issues related to suitability for a particular opticalswitching application, size, ease of fabrication, relaxing mechanicaltolerances for assembly of the reflective switching module 100,reliability, cost, etc. Specifically, the trapezoidally-shaped,convergent beam N×N reflective switching module 100 with the W-shapedfree space optical path illustrated in FIG. 7 is presently preferredbecause:

1. it fits within a standard twenty-three (23) inch widetelecommunications rack;

2. mechanical tolerances are acceptable;

3. long effective relay length for the beams of light 108; and

4. runs for electrical cables and optical cables are well separated.

As described above, the beam of light 108 produced by the lens 112 fromlight emitted from the end 104 of the associated optical fiber 106 firstimpinges upon the associated mirror surface 116 of one of the torsionalscanners included in the sets 118 a and 118 b. As described in greaterdetail below, for the configuration of the N×N reflective switchingmodule 100 depicted in FIG. 7, the mirror surfaces 116 are preferablyprovided by thirty-six (36) linear strips of thirty-two (32) torsionalscanners. Preferably, all thirty-two (32) mirror surfaces 116 in eachstrip are substantially coplanar. As an example, within each stripimmediately adjacent mirror surfaces 116 may be spaced 3.2 mm apart, andthe immediately adjacent columns of mirror surfaces 116 are preferablyspaced 3.2 mm apart with respect to the beams of light 108 impingingthereon from the immediately adjacent sides 102 a and 102 b.

Also for various configurations of the N×N reflective switching module100, the ends 104 of the optical fibers 106, the lenses 112, and themirror surfaces 116 of un-energized torsional scanners are preferablyoriented so all of the beams of light 108 produced by light emitted fromoptical fibers 106 having their ends 104 at the side 102 a preferablyconverge at a point 122 b that is located behind the set 118 b of mirrorsurfaces 116 in the illustrations of FIGS. 2 and 7. Correspondingly, thebeams of light 108 emitted from optical fibers 106 having their ends 104at the side 102 b in those FIGs. preferably converge at a point 122 athat is located behind the set 118 a of mirror surfaces 116. However,the location of the point at which the beams of light 108 convergedepend upon specific details of the N×N reflective switching module 100.For example, in the configuration of the N×N reflective switching module100 illustrated in FIG. 6a the beams of light 108 preferably converge ata point 122 that is located approximately behind a juncture of the sets118 a and 118 b.

Horizontally the convergence point 122 is established by consideringmirror surfaces 116 at opposite sides of the sets 118 a and 118 b. Thepoint 122 lies at the intersection of two lines that respectively bisectangles having their vertices at those two mirror surface 116 and sideswhich extend from the respective mirror surfaces 116 through mirrorsurfaces 116 at opposite ends of the other set 118 b or 118 a. The point122 is located vertically one-half the height of the sets 118 a and 118b. The geometrical arrangement of the ends 104 of the optical fibers106, the lenses 112, and the mirror surfaces 116 which produces thepreceding convergence provides equal clockwise and counter-clockwiserotation angles and minimal rotation angles for mirror surfaces 116 foreach of the sets 118 a and 118 b that exhibit the greatest movement inreflecting a beam of light 108 from one mirror surface 116 in the set118 a or 118 b to any of the mirror surfaces 116 in the other set 118 bor 118 a. If in the configuration for the N×N reflective switchingmodule 100 depicted in FIG. 7 a pair of mirror surfaces 116 a and 116 bare separated six-hundred and fifty (650) mm along the beam of light108, then the maximum angular rotation of the mirror surfaces 116 isapproximately 3.9° clockwise and counter-clockwise.

Although individual pairs of optical fibers 106 and lenses 112 could beinserted into grooves to assemble the sides 102 a and 102 b which yieldthe convergence of the beams of light 108 described in the precedingparagraph, for maximum density of lenses 112 and optical fibers 106 amonolithic block is preferably used that has holes appropriatelypre-drilled therein. Each pre-drilled hole receives one of the lenses112 and a conventional optical fiber ferrule secured about the end 104of one optical fiber 106. The compound angles required to align theoptical fiber 106 and the lens 112 for 2D convergence of the beams oflight 108 are provided by suitably orienting the holes drilled into theblock.

FIG. 8a depicts a preferred, cylindrically shaped micro-lens 112fabricated with its focal point at, or as close as possible to, a face138 of the lens 112. As those skilled in the art of fiber optics willunderstand, the optical fiber 106 emits the beam of light 108 at anangle with respect to a center line of the optical fiber 106 because theend 104 is polished at an angle to eliminate reflections back from theend 104. Because the end 104 is angled, the axis of the beam of light108 emitted from the end 104 diverges from the longitudinal axis of theoptical fiber 106. To align the beam of light 108 with a longitudinalaxis 144 of the lens 112, the face 138 of the lens 112 is angled tocenter the beam of light 108 within the lens 112. With the focal pointof the lens 112 at the face 138 as described above, the end 104 of theoptical fiber 106 is positioned one Raleigh range of the beam of light108, e.g. 50-60 microns, from the face 138. The diameter of acylindrical surface 136 of the lens 112 is made sufficiently large tocontain the diverging beam of light 108 before it exits the lens 112through a convex surface 142 as the quasi-collimated beam of light 108.

This configuration for the lens 112 and the end 104 of the optical fiber106 centers the beam of light 108 about the longitudinal axis 144 of thelens 112 at the convex surface 142 of the lens 112, with thequasi-collimated beam of light 108 oriented essentially parallel to thelongitudinal axis 144. Usual manufacturing tolerances for the lens 112described above produce acceptable deviations in exit angle and offsetof the beam of light 108 from the longitudinal axis 144 of the lens 112.For example, if the lens 112 is fabricated from BK7 optical glass andthe end 104 of the optical fiber 106 angles at 8°, then the angle of thebeam of light 108 within the lens 112 is 6.78°, and the lateral offsetfrom the longitudinal axis 144 is less than 50 microns both at the face138 and also 140 mm from the face 138. Such a well centered beam oflight 108 permits reducing the diameter of the surface 136 thus allowingthe lenses 112 to be placed closer to each other. This lens 112 ispreferably made from Gradium material marketed by LightPathTechnologies, Inc.

FIG. 8b depicts an alternative embodiment “champagne cork” shapedmicro-lens 112 which advantageously permits spacing lenses 112 andoptical fibers 106 closer together at the sides 102 a and 102 b. Thelens 112 includes a smaller diameter surface 132 which aconically-shaped optical fiber collimator assembly 134 illustrated inFIG. 9 receives. The larger diameter surface 136 of the lens 112protrudes out of the optical fiber collimator assembly 134. Thechampagne cork shaped embodiment of the microlens 112 may be fabricatedby grinding down a portion of the lens 112 illustrated in FIG. 8a.

As illustrated in FIG. 9, in addition to receiving one of either thecylindrically shaped lens depicted in FIG. 8a or the champagne corkshaped micro-lens 112 depicted in FIG. 8b, each optical fiber collimatorassembly 134 also provides a receptacle that receives a conventionalfiber optic ferrule 146 secured about the end 104 of the optical fiber106. A convergence block 152, one of which is respectively disposed atboth sides 102 a and 102 b of the reflective switching module 100, ispierced by a plurality of conically shaped holes 154 as illustrated inFIG. 10 that equal in number to the number N of optical fibers 106.Convergence of the beams of light 108 as described above is effected bythe alignment of the optical fiber collimator assemblies 134 uponinsertion into the holes 154. The optical fiber collimator assemblies134 and holes 154 are preferably formed from the same material withidentically shaped, mating, conical surfaces that taper at an angle of afew degrees. Configured in this way, when all optical fiber collimatorassemblies 134 carrying the optical fibers 106 are fully seated intotheir mating holes 154, the optical fiber collimator assemblies 134becomes fixed in the convergence block 152 and hermetically seal theinterior of the reflective switching module 100 through which thequasi-collimated beams of light 108 propagate.

The convergence block 152 may be simply machined out a single piece ofmetal such as stainless steel, or from a ceramic material, etc.Alternatively, the convergence block 152 may be made out of Kovar, 42%nickel-iron alloys, titanium (Ti), tungsten (W) or molybdenum (Mo)suitably plated for corrosion resistance. These materials all havecoefficients of expansion which approximately match that of the lenses112 and minimize birefringent effects that may take place as lenses 112are heated or cooled in their operating environment.

In addition to the preceding preferred way of providing convergence bysuitably orienting the optical fibers 106 and the lenses 112 at each ofthe sides 102 a and 102 b, either 1D or 2D convergence may also beobtained in other ways. For example, the configuration of the opticalfibers 106 and the lenses 112 could provide some of the convergencewhich the arrangement of the mirror surfaces 116 upon which the beams oflight 108 first impinge could provide the remainder of the convergence.For example the mirror surfaces 116 in each column could be arrangedalong a cylindrical surface. Alternatively, the optical fibers 106 andthe lenses 112 might be arranged to provide none of the convergence,i.e. beams of light 108 propagate parallel from the sides 102 a and 102b to the first mirror surfaces 116, with the mirror surfaces 116 beingarranged to provide all of the convergence as illustrated in FIGS. 4a-4b. For example the mirror surfaces 116 in each column could be arrangedalong a spherical surface. Moreover, the optical fibers 106, lenses 112,and sets 118 a and 118 b of mirror surfaces 116 may be arranged toprovide either 1D or 2D convergence either behind the sets 118 a and 118b or at the sets 118 a and 118 b. With regard to the various alternativeways of arranging convergence of the beams of light 108, selecting oneway in comparison with other possible ways usually involves issuesrelated to ease of fabrication, relaxing mechanical tolerances forassembly of the reflective switching module 100, reliability, cost, etc.

Machining the convergence block 152 out a single piece of metal asdescribed previously to provide convergence for the beams of light 108means that individual holes 154 are under compound complex angles withrespect to each other. The beam of light 108 emitted from each opticalfiber collimator assembly 134 must be oriented to impinge directly onthe mirror surface 116 immediately in front of the lens 112. If the beamof light 108 misses the mirror surface 116 slightly, the beam of light108 will loose a substantial amount of power during during transmissionthrough the reflective switching module 100. In fact, a substantialmisalignment between the beam of light 108 emitted from a particularlens 112 and the corresponding mirror surface 116 might render theoptical fiber 106 inoperable. Consequently, alignment of each beam oflight 108 with its corresponding mirror surface 116 is essential forproper operation of the reflective switching module 100.

As stated previously, the end 104 of each optical fiber 106 ispositioned at the focal length of the lens 112 plus the Raleigh range ofthe beam of light 108 emitted from the optical fiber 106. The lens 112typically exhibits more centration error. Furthermore, it is alsopossible that the longitudinal axis 144 of the lens 112 tilts slightlywith respect to the optical fiber 106 due to variations in the lens 112and the optical fiber collimator assembly 134. A possibility also existsthat the ferrule 146 and the lens 112 may be misaligned. For all ofthese reasons, a structure that provides an alternative to the structuredepicted in FIGS. 9 and 10, and which permits adjusting the position andorientation of the lens 112 is highly desirable.

Usually, the hole 154 that receives the lens 112 and the optical fiber106 is drilled in solid material forming the convergence block 152 asillustrated in FIG. 10a. After drilling the holes 154, to provide analternative convergence block 152 a face 156 thereof is then slit invarious directions through the holes 154 to a depth slightly greaterthan the length of the lenses 112. After slitting, more material may beremoved from the face 156 around each hole 154 so each lens 112 may beheld by three (3) arcuate, deforable posts 157 as illustrated in FIG.10b. This provides a mounting for the lens 112 that is monolithicallyintegrated into the convergence block 152, protrudes outward from it,and is plastically deformable.

The lenses 112 are initially secured in the convergence block 152preferably by impact centration. During impact centration, the posts 157flow around the lens 112, and hold the lens 112 in place. Then, ferrules146, each respectively carrying the end 104 of one optical fiber 106,are inserted into individual holes 154 in the convergence block 152. Theferrules 146 are then adjusted length wise within the holes 154 so eachbeam of light 108 focuses at the proper place within the reflectiveswitching module 100, which is typically halfway between the sets 118 ofmirror surfaces 116. After focusing, each ferrule 146 is then preferablyfixed to the convergence block 152 by impact. This system for impactmounting of optical fibers 106 can produce an alignment with 2 micronsof concentricity between the ferrule 146 and the optical fiber 106. Theconcentricity between the ferrule 146 and the hole 154 may also be heldto a few microns.

With the lenses 112 and optical fibers 106 now fixed in the convergenceblock 152, the posts 157 holding each of the lenses 112 can now bedeformed so each lens 112 aligns exactly with the corresponding opticalfiber 106. During such alignment, the beam of light 108 emitted from thelens 112 is monitored using a camera or by some other means whileorienting the beam of light 108 by plastically deforming the supportingposts 157. In this way, each lens 112 may be tilted and displaced so thebeam of light 108 emitted therefrom impinges directly on the mirrorsurface 116 immediately in front of the lens 112.

In most telecommunication installations, optical fibers are generallymatched as a duplex pair in which one fiber carries communications inone direction while the other fiber of the pair carries communicationsin the opposite direction. Connectors adapted for coupling light betweentwo duplex pairs of optical fibers which secure the two optical fibersof a pair in a single ferrule are presently available. Because bothoptical fibers of a duplex pair are switched concurrently, and becausethe reflective switching module 100 can couple light in either directionbetween a pair of optical fibers 106 one of which is respectivelylocated at side 102 a and the other of which is located at side 102 b,suitably adapting the lenses 112 for use with duplex pairs of opticalfibers 106 permits using a single pair of mirror surfaces 116 a and 116b for switching light carried in opposite directions respectively in thetwo optical fibers 106 of the duplex pair.

FIG. 11 depicts a lens 112 adapted for use in the reflective switchingmodule 100 for concurrently switching light carried by a duplex pair ofoptical fibers 106 a and 106 b. As illustrated in FIG. 11, the duplexoptical fiber ferrule 146 carries the duplex pair of optical fibers 106a and 106 b. The ends 104 a and 104 b of the optical fibers 106 a and106 b and the faces 138 a and 138 b of the lens 112 are all polished atan angle. The angles of the faces 138 a and 138 b are formed tocompensate for the off-axis position of the optical fibers 106 a and 106b so beams of light 108 a and 108 b impinging upon faces 138 a and 138 bfrom the optical fibers 106 a and 106 b are formed into quasi-collimatedbeams which exit the convex surface 142 parallel to but slightly offsetfrom the longitudinal axis 144, and propagate in that way through thereflective switching module 100. Both of the beams of light 108 a and108 b impinge upon the same pair of mirror surfaces 116 a and 116 bwhich are made large enough to simultaneously reflect both beams oflight 108 a and 108 b. When the two quasi-collimated beams of light 108a and 108 b impinge upon another identically configured lens 112 andduplex pair of optical fibers 106 at the opposite side 102 a or 102 b ofthe reflective switching module 100, the lens 112 located there couplesthe beams of light 108 a and 108 b into the respective optical fibers106 of the duplex pair.

As described above, the mirror surfaces 116 a and 116 b of the sets 118a and 118 b are preferably provided by electrostatically energized 2Dtorsional scanners of a type described in the '790 patent. U.S. patentapplication Ser. No. 08/885,883 filed May 12, 1997, and published PatentCooperation Treaty (“PCT”) Patent Application International PublicationNumber: WO 98/44571, both of which are also incorporated by reference,provide additional more detailed information regarding the preferred 2Dtorsional scanner. Hinges which permit the mirror surfaces 116 to rotateabout two (2) non-parallel axes preferably include torsion sensors of atype disclosed in U.S. Pat. No. 5,648,618 (“the '618 patent”) that isalso incorporated herein by reference. The torsion sensors included inthe hinges measure rotation of a second frame or a plate, that has beencoated to provide the mirror surface 116, respectively with respect tothe first frame or with respect to the second frame.

As described in the patents and patent applications identified above,torsional scanners are preferably fabricated by micro-machining singlecrystal silicon using Simox, silicon-on-insulator or bonded siliconwafer substrates. Such wafer substrates are particularly preferredstarting material for torsional scanner fabrication because they permiteasily fabricating a very flat, stress-free membrane, possibly only afew microns thick, which supports the mirror surfaces 116. Asillustrated in FIG. 12, a silicon-on-insulator (“SOI”) wafer 162includes an electrically insulating silicon dioxide layer 164 thatseparates single crystal silicon layers 166 and 168. Torsion bars andplates that carry the mirror surfaces 116 of torsional scanners areformed in the thinner device silicon layer 166 while other portions oftorsional scanners are formed by backside etching in the thicker handlesilicon layer 168. As is well known to those skilled in the art ofmicro-machining, the device silicon layer 166 has a frontside 169furthest from the handle silicon layer 168 and a backside 170 at thesilicon dioxide layer 164. The intermediate silicon dioxide layer 164provides a perfect etch stop for etching the wafer 162 from itsbackside, and yields torsion bars and plates having uniform thickness.

FIG. 13 depicts a single electrostatically energized 2D torsionaltorsional scanner 172 adapted for providing the mirror surfaces 116 forthe reflective switching module 100. The torsional scanner 172 includesan outer reference frame 174 to which are coupled a diametricallyopposed pair of outer torsional flexure hinges 176. The torsionalflexure hinges 176 support an inner moving frame 178 for rotation aboutan axis established by the torsional flexure hinges 176. A diametricallyopposed pair of inner slotted torsion-bar hinges 182 couple a centralplate 184 to the inner moving frame 178 for rotation about an axisestablished by the torsion-bar hinges 182. The axes of rotationestablished respectively by the torsional flexure hinges 176 and by thetorsion-bar hinges 182 are non-parallel, preferably perpendicular.

It is important to note that the plate 184 of the torsional scanner 172is rectangularly shaped with the longer side being approximately 1.4times wider than the height of the plate 184. The plate 184 included inthe reflective switching module 100 has a rectangular shape because thebeam of light 108 impinges obliquely at an angle of 45° on the mirrorsurface 116 carried by the plate 184. Consequently, for reflection ofthe beam of light 108 from the mirror surface 116 the rectangularlyshaped plate 184 becomes effectively square. The plate 184 is preferably2.5 mm×1.9 mm, and is typically between 5 and 15 microns thick as arethe inner moving frame 178, the torsional flexure hinges 176 andtorsion-bar hinge 182. The torsional flexure hinges 176 and torsion-barhinge 182 are between 200 and 400 microns long, and between 10 and 40microns wide. The resonance frequencies on both axes are on the order of400 to 800 Hz which permits switching a beam of light 108 between twooptical fibers 106 in approximately 1 to 5 milliseconds. Both thefrontside 169 and the backside 170 of the plate 184 are coated inperfect stress balance with identical metallic adhesion layers,preferably 10.0 to 100.0 A° of titanium (Ti) or zirconium (Zr) whichunderlie a 500 to 800 A° thick metallic reflective layer of gold (Au).

The torsional flexure hinges 176, which are illustrated in greaterdetail in FIG. 14a, provide various advantages in comparison with aconventional unfolded torsion bar. A United States patent applicationand a Patent Cooperation Treaty (“PCT”) international patentapplication, which are both entitled “Micromachined Members Coupled forRelative Rotation by Torsional Flexure Hinges,” which were both filedSep. 2, 1999, by Timothy G. Slater and Armand P. Neukermans and whichare both incorporated herein by reference, describe the variousadvantages provided by the torsional flexure hinges 176. Mostsignificant for the reflective switching module 100, the torsionalflexure hinges 176 are more compact than a conventional unfolded torsionbar having an equivalent torsional spring constant.

The torsion-bar hinges 182, which are illustrated in greater detail inFIG. 14b, superficially resemble a conventional torsion bar hinge.However, differing from the conventional torsion bar hinge, thetorsion-bar hinges 182 are pierced by several longitudinal slits 186,e.g. four (4) or five (5), that are oriented parallel to the length ofthe torsion-bar hinges 182. The slits 186 subdivide a single torsion barinto a number of much thinner individual bars that are much thicker thantheir width. Similar to the torsional flexure hinges 176, thetorsion-bar hinges 182 are more compact than a conventional one-piecetorsion bar having an equivalent torsional spring constant. However, inconformance with the disclosure in U.S. Pat. No. 5,629,790 thetorsion-bar hinges 182 provide more mode separation between theprincipal torsional vibration mode and the higher order modes than thetorsional flexure hinges 176. Moreover, the torsion-bar hinges 182 aremuch stiffer than the torsional flexure hinges 176 in a directionperpendicular to the plate 184. Consequently, use of the torsionalflexure hinges 176 and torsion-bar hinges 182 instead of a conventionalunfolded torsion bar permits making much smaller torsional scanners 172that can be packed more closely together which correspondingly increasesthe number of optical fibers 106 that may be accommodated at the sides102 a and 102 b of the reflective switching module 100.

Each torsional scanner 172 included in the reflective switching module100 includes a pair of torsion sensors 192 a and 192 b, of a typedisclosed in the '618 patent. The torsion sensors 192 a and 192 bmeasure orientation of the supported member, i.e. the plate 184 or theinner moving frame 178, with respect to the supporting member, i.e. theinner moving frame 178 or the outer reference frame 174, at atheoretical resolution of approximately 1.0 micro-radians. In accordancewith the description in the '618 patent, when the torsional scanner 172is operating in the reflective switching module 100 an electricalcurrent flows in series through the two torsion sensors 192 a and 192 bbetween a pair of sensor-current pads 194 a and 194 b. Accordingly, thetorsional scanner 172 includes a meandering metal conductor 196 that isbonded to the frontside 169 of the device silicon layer 166. Starting atthe sensor-current pad 194 a, the meandering metal conductor 196 crossesthe immediately adjacent torsional flexure hinge 176 from the outerreference frame 174 onto the inner moving frame 178 to reach the X-axistorsion sensor 192 b that is located in the lower torsion-bar hinge 182.From the X-axis torsion sensor 192 b the meandering metal conductor 196continues onto a reflective, stress balanced metal coating, that isapplied to both sides of the plate 184 to provide the mirror surface116, and across the plate 184 and the upper torsion-bar hinge 182 backonto the inner moving frame 178. The meandering metal conductor 196 thenleads to the Y-axis torsion sensor 192 a that is located in the lefthand torsional flexure hinge 176. From the Y-axis torsion sensor 192 a,the meandering metal conductor 196 then curves around the outerreference frame 174 to the sensor-current pad 194 b. Metal conductors,that are disposed on opposite sides of the meandering metal conductor196 across the right hand torsional flexure hinge 176 and on the innermoving frame 178, connect a pair of inner-hinge sensor-pads 198 a and198 b to the X-axis torsion sensor 192 b. Similarly, metal conductors,one of which is disposed along side the meandering metal conductor 196on the outer reference frame 174 and the other with curves around theopposite side of the torsional scanner 172 on the outer reference frame174, connect a pair of inner-hinge sensor-pads 202 a and 202 b to theY-axis torsion sensor 192 a. A pair of grooves 204, cut only through thedevice silicon layer 166 on opposite sides of the inner-hingesensor-pads 198 a and 198 b, increase electrical isolation between thesensor-current pad 194 a and the inner-hinge sensor-pads 198 a and 198 band the sensor-current pad 194 b and the inner-hinge sensor-pads 202 aand 202 b.

Preferably, the backside 170 of the plate 184 provides the mirrorsurface 116 because, as illustrated in FIG. 15, the frontside 169 facesan insulating substrate 212 which carries both electrodes 214 used inenergizing rotation of the plate 184 and contacts for the sensor-currentpads 194 a and 194 b, the inner-hinge sensor-pads 198 a and 198 b andthe inner-hinge sensor-pads 202 a and 202 b not illustrated in FIG. 15.The plates 184 of each torsional scanner 172 are separated a distance,e.g. from 40 to 150 microns, from the substrate 212 by spacers which arealso not depicted in FIG. 15. The separation between the plate 184 andthe substrate 212 depends upon how far edges of the plate 184 moveduring rotation.

Note that for the reflective switching module 100 very thin plates 184,only a few microns thick, are desirable and can be fabricated using thedevice silicon layer 166 of the wafer 162. In many instances the plate184 and the torsional flexure hinges 176 and torsion-bar hinge 182 canbe made of the same thickness as the device silicon layer 166.Alternatively, as illustrated in FIG. 15 the torsional flexure hinges176 may be thinned by etching. For example, the torsional flexure hinges176 may be 6 microns thick while the plate 184 may be 10 microns thick.Analogously, the plate 184 may be thinned to reduce its moment ofinertia by etching a cavity 216 into the plate 184 leaving reinforcingribs 218 on the thinned plate 184.

A telecommunication system component such as the reflective switchingmodule 100 must exhibit high reliability. A plate 184 of the torsionalscanner 172 that accidentally collides with the electrode 214 should notstick to it, and should immediately rotate to its specified orientation.Furthermore, such accidental collisions should not damage the torsionalscanner 172, or any circuitry connected to the torsional scanner 172. Topreclude stiction, as illustrated in FIG. 13 the periphery of the plate184 and of the inner moving frame 178 have rounded corners that reducethe strength of the electrostatic field. Rounding the periphery of theplate 184 also reduces its effective turning radius which results fromcompound rotation of the plate 184 about the axes respectivelyestablished by both torsional flexure hinges 176 and torsion-bar hinge182.

In addition to rounding the periphery of the plate 184 and the innermoving frame 178, as illustrated in FIG. 15a locations where the plate184 may contact the electrodes 214 are overcoated with electricalinsulating material 219 such as polyimide. Overcoating only thoseportions of the electrodes 214 which may contact the plate 184 with theelectrical insulating material 219 avoids charge stored on most of theelectrodes 214. Analogously, during fabrication of the torsional scanner172 some of the silicon dioxide layer 164 may be left at the peripheryof the plate 184 50 the metallic reflective layer which provides themirror surface 116 never contacts the electrode 214. Alternatively, asillustrated in FIG. 16b holes 220 are formed through the metal of theelectrodes 214 in areas of possible contact.

During operation of the reflective switching module 100, the torsionalscanner 172 is at a ground electrical potential while driving voltagesare applied to the electrodes 214. To reduce electrical dischargecurrents if the plate 184 contacts the electrodes 214, large resistors(e.g. 1.0 MΩ) may be connected in series with the driving circuit forthe electrodes 214. Ideally these resistors should be located as closeas practicable to the electrodes 214 otherwise the conductor connectingbetween the electrodes 214 and the resistors might pickup stray electricfields that rotate the plate 184. Therefore, one alternative is toovercoat the electrodes 214 with a very high resistivity but slightlyconductive material in selected areas such as those illustrated in FIG.16a to provide a bleed path from the electrodes 214 for DC charges.Furthermore, inputs of all amplifiers connected to torsional scanners172, such as those which receive orientation signals from the torsionsensors 192 a and 192 b, should include diode protection to preventdamage from an over-voltage condition due to arcing or accidentalcontact between the plate 184 and the electrodes 214.

Several configurations exist that may be exploited advantageously toincrease the density of the mirror array, which is usually the limitingfactor on the density of optical fibers 106 at the sides 102 a and 102b. For several reasons, particularly the large number of contacts thatmust be brought out for each torsional scanner 172, the torsionalscanners 172 are preferably arranged into strips 222 as illustrated inFIGS. 16a and 16 b. Organizing the torsional scanners 172 into strips222 increases their density above that which might be achieved ifarranged as a 2 dimensional array of discrete torsional scanners 172.Each strip 222 includes a metal support frame 224 to which the substrate212 is fastened.

As explained in greater detail below, the strip 222 is flip-chip bondedto the substrate 212 so all electrical connections to the strip 222 aremade between the strip 222 and the substrate 212. A flat polyimidebacked multi-conductor ribbon cable 226 connects to the substrate 212 toexchange electrical signals between the pads 194, 198 and 202 and theelectrodes 214. Since each support frame 224 may be an open framepossibly including reinforcing ribs, the ribbon cable 226 can be freelybent and guided away from the substrate 212.

FIG. 16b illustrates how, without obscuring the mirror surfaces 116, thesubstrates 212 and the strips 222 may be overlapped with the ribboncable 226 serpentined along the staircased substrates 212. Arranging thestrips 222 in this way reduces the horizontal distance between themirror surfaces 116 of immediately adjacent strips 222 in relationshipto the beams of light 108. Since the beams of light 108 impinge upon themirror surfaces 116 at approximately 450, the apparent distance betweenimmediately adjacent strips 222 is further foreshortened by a factor ofapproximately 1.4 which, as described above, is why the plate 184 ispreferably rectangularly shaped.

One disadvantage with the configuration of strips 222 illustrated inFIG. 16b is that the offset between immediately adjacent strips 222cannot be less than the thickness of the torsional scanners 172 plus thesubstrate 212. Furthermore, overlapping of immediately adjacent strips222 and substrates 212 hinders removing a single defective strip 222without disturbing immediately adjacent strips 222.

FIGS. 16c and 16 d illustrate a preferred embodiment for the strips 222and the support frames 224 in which electrical leads 228 that connect tothe torsional scanners 172 are preferably provided by electricallyconductive vias formed through the substrate 212. Alternatively, theleads 228 can be plated or screened onto one face, around one edge, andonto the other face of the substrate 212. With this configuration forthe leads 228, attachment of the ribbon cable 226 to the substrate 212is unhindered. Plating or screening the leads 228 onto the substrate 212and including some via holes through the substrate 212 permits thesubstrate 212 to be as narrow as the strip 222. Narrowed to this extent,the combined strips 222, substrates 212 and support frames 224 may nowbe arranged as illustrated in FIG. 16e for both of the sets 118 a and118 b. This permits the offset between immediately adjacent strips 222to be established as required by the optics of the reflective switchingmodule 100 rather than by packaging considerations. The optimum offsetbetween immediately adjacent strips 222 is approximately 0% to 10% ofthe distance between plates 184 in immediately adjacent strips 222. Theconfiguration of the substrate 212 illustrated in FIG. 16d facilitatesaccess to the substrate 212 and removal of the strip 222 withoutdisturbing adjacent support frames 224. Note that if necessary the leads228 may be brought out around both edges of the substrate 212. Thiscapability may be exploited advantageously to separate leads 228carrying high voltage driving signals that are applied between the plate184 and the electrodes 214 from leads 228 which carry signals from thetorsion sensors 192 a and 192 b.

The ribbon cables 226 can be attached to the substrates 212 asillustrated in FIGS. 16d and 16 e by hot bar bonding.

Electrical connections between the leads 228 on the substrate 212 andthe multi-conductor ribbon cables 226 can be provided by solder, or,preferably, by anisotropically electrically conductive film. Themechanical attachment of the ribbon cable 226 to the substrate 212 canbe reinforced by a strain-relief bead 229 of epoxy.

Without reducing the size of the plate 184, as illustrated in FIG. 17athe density of the optical fibers 106 at the sides 102 a and 102 b maybe increased by offsetting the torsional scanners 172 of immediatelyadjacent strips 222 vertically by one-half the vertical distance betweentorsional scanners 172 within the strip 222. Due to the convergencecriteria set forth above for arranging the beams of light 108 within thereflective switching module 100, offsetting the torsional scanners 172in immediately adjacent strips 222 effects a reorganization of the holes154 which receive the optical fiber collimator assemblies 134 from aquasi rectangular array into a quasi hexagonally close packed array.While offsetting the torsional scanners 172 in immediately adjacentstrips 222 does not increase the density of the torsional scanners 172,such an arrangement of the torsional scanners 172 does increase thedensity of the optical fibers 106 at the sides 102 a and 102 b to theextent that the diameter, either of lenses 112 or of optical fibercollimator assemblies 134, limits the spacing between immediatelyadjacent optical fibers 106.

The density of torsional scanners 172 may be even further increased byfabricating the torsional scanners 172 as completely monolithic twodimensional arrays rather than as strips 222. As illustrated in FIG.17b, offsetting the torsional scanners 172 in immediately adjacentcolumns permits interdigitation of the torsional flexure hinges 176 oftorsional scanners 172 into an empty space that occurs between torsionalscanners 172 in immediately adjacent columns or rows of the array. Thisinterdigitating of the torsional flexure hinges 176 provides a shorterdistance between centers of plates 184 of torsional scanners 172 inadjacent columns or rows, and more closely approximates a hexagonalclose packing of the torsional scanners 172 and, correspondingly, of theoptical fibers 106 at the sides 102 a and 102 b.

An alternative embodiment for strips 222 orients the torsional flexurehinges 176 and torsion-bar hinge 182 at 450 with respect to the verticaland horizontal axes of the support frame 224. FIGS. 18a and 18 billustrate a diagonal configuration for the torsional flexure hinges 176and torsion-bar hinge 182 which more efficiently uses area on the strips222 than a configuration in which the torsional flexure hinges 176 andtorsion-bar hinge 182 are oriented parallel and perpendicular to strips222. Using a diagonal orientation for the torsional flexure hinges 176and torsion-bar hinge 182 oriented at 45° with respect to the outerreference frame 174, they can be longer without increasing the areaoccupied by the torsional scanner 172. The plate 184 is elongated in onedirection to accommodate the 450 impingement angle of the beam of light108. Due to the elliptical shape of the beam of light 108 as it impingesupon the plate 184, corners of the beam of light 108 may be eliminatedresulting in an octagonally shaped plate 184, which convenientlyprovides room for the outer reference frame 174. Sides of the outerreference frame 174 are oriented in the <110> crystallographic directionof silicon for ease of fabrication. This configuration for the torsionalscanner 172 orients the torsion sensors 192 a and 192 b along the <100>crystallographic direction of silicon. Thus, a wafer 162 having a p-typedevice silicon layer 166 or p-type implantation must be used infabricating the torsion sensors 192 a and 192 b. The <110> and <100>crystallographic directions of silicon may be interchanged with suitableprocess changes.

Using the arrangement of the torsional scanner 172 illustrated in FIG.18b, 1.5×2 mm plates 184 may be spaced only 2.5 mm apart effectivelyincreasing the density of mirror surfaces 116 by a factor of 1.4. Whenviewed at the approximate 45° incident angle of the beams of light 108,the strips 222 slope at 54°. In this configuration the strips 222 areoriented at 45° to the support frames 224. This orientation of thestrips 222 is necessary if the mirror surfaces 116 are to fullyintercept the beams of light 108. The support frames 224 could beoriented at 45° which permits all the strips 222 to be the same length,thereby using area on wafers 162 more efficiently.

FIG. 19a illustrates yet another alternative embodiment of the torsionalscanner 172 which further reduces its size thereby further shorteningdistances between immediately adjacent mirror surfaces 116 in thereflective switching module 100. From the preceding description it isapparent that positioning the torsional flexure hinges 176 andtorsion-bar hinge 182 at corners rather than sides of the plate 184advantageously reduces the size of the torsional scanner 172. In FIG.19a an elliptically-shaped curve 232 represents an outline of the beamof light 108 impinging on the mirror surface 116 of the plate 184.Because the beam of light 108 does not impinge on the corners of theplate 184, the inner torsion-bar hinges 182 may be rotated with respectto the plate 184 to occupy unused corner space. As in the configurationof the torsional scanner 172 illustrated in FIG. 1a, the outer torsionalflexure hinges 176 continues to occupy corners of the outer referenceframe 174.

Not only does placement of the torsion-bar hinges 182 at the corners ofthe plate 184 as illustrated in FIG. 19a reduce the size of thetorsional scanner 172, it also reduces compounding of the angles whenthe plate 184 rotates simultaneously about both axes. Compoundingincreases the distance through which corners of the plate 184 move whenthe plate 184 simultaneously rotates about axes established by bothtorsional flexure hinges 176 and torsion-bar hinge 182. Compoundingincreases the separation required between the plate 184 and thesubstrate 212 which correspondingly increases the voltage that must beapplied between the plate 184 and the electrodes 214 for equivalentperformance in rotating the plate 184. However, if the plate 184 has anaspect ratio that is not square as will usually occur for plates 184included in the reflective switching module 100, then the torsionsensors 192 a and 192 b in torsional flexure hinges 176 and torsion-barhinge 182 depicted in FIG. 19a are no longer oriented along orthogonalcrystallographic directions, i.e. either <100> or <110> directions, ofsilicon. This is undesirable, since the torsion sensors 192 a and 192 bin the torsional flexure hinges 176 and torsion-bar hinge 182 thenrespond both to bending and torsion of the torsional flexure hinges 176and torsion-bar hinge 182.

Because the plate 184 depicted in FIG. 19a has an aspect ratio ofapproximately 1.4:1, axes of rotation 236 a and 236 b established by thetorsional flexure hinges 176 and torsion-bar hinge 182 intersect atapproximately 70.5°. However, reorienting the axes of rotation 236 a and236 b slightly until they intersect at 90°, as illustrated in FIG. 19b,permits the torsional flexure hinges 176 and torsion-bar hinge 182 to beoriented along a single crystallographic direction of silicon, e.g. the<100> crystallographic orientation if the outer reference frame 174 isaligned along the <110> crystallographic direction of silicon.Configured as illustrated in FIG. 19b, the torsional scanner 172provides a significant amount of space for the inner torsion-bar hinges182 in the corners of the plate 184 which reduces the size of thetorsional scanner 172. Furthermore, the configuration of the torsionalscanner 172 illustrated in FIG. 19b preserves the crystallographicorientation of the torsion sensors 192 a and 192 b while the compoundingeffect, though not completely eliminated, is significantly reduced.However, in the configuration of the torsional scanner 172 depicted inFIG. 19, the orthogonal axes of rotation established by the torsionalflexure hinges 176 and torsion-bar hinge 182 are oriented obliquely tothe length and width of the plate 184. Nevertheless, because only smallangular rotations of the plate 184 occur during operation of thereflective switching module 100 the area of the plate 184 upon which thebeam of light 108 impinges changes insignificantly when the plate 184rotates.

Incorporating the torsional scanners 172 illustrated in FIG. 18a or 19 ainto one of the set 118 a or 118 b of mirror surfaces 116 to maximizetheir respective advantages requires rearranging the shape of the set118 a or 118 b. A preferred arrangement for strips 222′ of torsionalscanners 172 depicted in FIG. 18a is illustrated in FIG. 20a. Asdescribed above and depicted FIG. 20a, the strips 222′ are mounted at a45° angle with respect to a horizontal base 242 of the reflectiveswitching module 100. In the illustration of FIG. 20a, the supportframes 224′ carrying the strips 222′ are also mounted at a 45° anglewith respect to the base 242. The two axes established by the torsionalflexure hinges 176 and torsion-bar hinge 182 about which the plates 184rotate are indicated by x and y axes 244 depicted in FIG. 20a. Themaximum rotation angles for plates 184 about axes established by thetorsional flexure hinges 176 and torsion-bar hinge 182 allowed foridentical torsional scanners 172 at the other set 118 b or 118 a ofmirror surfaces 116 establishes a serrated rectangularly-shaped field246 of addressable torsional scanners 172 in the addressed set 118 a or118 b.

This optimum rectangularly-shaped field 246 is truncated at the cornersand has sides that are approximately diagonal to the strips 222′. Forthe arrangement illustrated in FIG. 20a, the longest strip 222′ mustinclude at least 1.4 times more torsional scanners 172 than thatrequired for a rectangular array of the torsional scanners 172 assembledfrom the strip 222 illustrated in FIG. 16a. However, torsional scanners172 may be omitted from locations in the set 118 a or 118 b that cannotbe addressed from the other set 118 b or 118 a. Thus, only a few of thestrips 222′ illustrated in FIG. 20a need be full length. Those strips222′ that include only a few torsional scanners 172 might even beeliminated entirely. For example by using 40 strips 222′ containing amaximum 44 torsional scanners 172, it is possible to arrange as many as1152 torsional scanners 172 in the set 118 a or 118 b, with very smallscan angles, and relatively small mirror sizes. A different arrangementprovides for 1132 torsional scanners 172, which measure only 1.59 by 2.2mm, and requires deflection angles of 3.69° and 3.3°. The strips 222′ ofthe torsional scanners 172 are oriented at an average of 55° to theoptical fiber collimator assemblies 134. The arrangement illustrated inFIG. 20a, though slightly more complex substantially increases thedensity of the torsional scanners 172 and, correspondingly, the opticalfiber collimator assemblies 134, and allows more scanners to beaddressed for particular rotation angles specified for the plates 184.

FIG. 20b illustrates an analogous re-arrangement at the sets 118 a and118 b of torsional scanners 172 of the type depicted in FIG. 19b. Forthis arrangement of the torsional scanners 172 depicted in FIG. 19b thestrips 222′ and the support frames 224″ are oriented vertically similarto the illustration of FIG. 16a. However, the x and y axes 244 aboutwhich the plate 184 rotate are oriented at 45° with respect to thestrips 222′ and their support frames 224″. The oblique orientation ofthe x and y axes 244 with respect to the strips 2221″ and the supportframes 224″ again means that the maximum rotation angles for plates 184of corresponding torsional scanners 172 at the other set 118 b or 118 aof mirror surfaces 116 establishes a serrated octagon or truncatedrectangularly-shaped field 256 of addressable torsional scanners 172 atthe addressed set 118 a or 118 b. If the rectangularly-shaped field 256established for these torsional scanners 172 is p×q, then the optimumfield coverage for strips is a square or rectangular field with an areaof 0.7 to 1.2 pq, symmetrically arranged along the diagonal x and y axes244. This results in an aspect ratio for the rectangularly-shaped field256 that is slightly elongated in the direction of the strips 222″, e.g.1.0:1.3. If the set 118 a or 118 b have horizontally oriented strips222″ and support frames 224″, then the elongation of therectangularly-shaped field 256 becomes horizontal rather than vertical.For manufacturing convenience, all strips 222″ are made the same length.Analogous to the arrangement of torsional scanners 172 depicted in FIG.20a, there again exist areas of the rectangularly-shaped field 256 whichcan omit torsional scanners 172. Again it is advantageous to omitshorter strips 222″ along the sides of the rectangularly-shaped field256 which have few torsional scanners 172, and to slightly elongateothers strips 222″. In the example illustrated in FIG. 20b, for a 1.8 by2.4 mm plate 184 and rotation angles for the plates 184 about the x andy axes 244 of 5.6° and 3.7° the arrangement significantly increases thenumber of torsional scanners 172 to approximately 1,500.

In the configurations of the reflective switching module 100 describedthus far, the optical fiber collimator assemblies 134 are fastened inthe convergence block 152 which is located some distance from at leastportions of the sets 118 a and 118 b of mirror surfaces 116. Thisconfiguration for the reflective switching module 100 requires very goodalignment of the optical fiber collimator assemblies 134 to the mirrorsurfaces 116. FIG. 21 illustrates an arrangement of whereby thecollimating lens 112, optical fibers 106 and strips 222 of torsionalscanners 172 are brought closer together thereby relaxing tolerances fortheir alignment. In that illustration, the substrate 212 is made widerthan the strip 222 and a mirror strip 262 attached to the surface of thesubstrate 212 opposite to the strip 222 to establish a beam-folding anddeflecting assembly 264. The beam-folding and deflecting assemblies 264are then arranged into a repeating, regular structure in which thequasi-collimated beam of light 108 reflecting off the mirror strip 262of one beam-folding and deflecting assembly 264 impinges upon the mirrorsurface 116 provided by the immediately adjacent torsional scanner 172.Since in the arrangement illustrated in FIG. 21 all the lenses 112 arelocated an identical short distance from their associated mirror surface116, alignment of the beams of light 108 to their respective mirrorsurfaces 116 is less critical.

Convergence of the beams of light 108 may be provided in one dimensionby tilting each mirror strip 262 slightly from a nominal 45° angle asillustrated schematically in FIG. 21a. Convergence in a second dimensionmay be obtained by appropriately orienting the optical fiber collimatorassemblies 134 with respect to their respective associated mirrorsurfaces 116 as illustrated schematically in FIG. 21b. Combining theseindividual one dimensional convergences produces the preferred twodimensional convergence described previously. Orientations for themirror strips 262 and for the optical fiber collimator assemblies 134may be chosen to produce the preferred convergence with identicalbeam-folding and deflecting assemblies 264 that are mounted at slightlydifferent angles with respect to each other. Because in the arrangementillustrated in FIG. 21 the substrates 212 are near their associatedmirror surface 116, almost the entire five-hundred (500) to nine-hundred(900) mm long path between the sides 102 a and 102 b is between pairs ofmirror surfaces 116 in the sets 118 a and 118 b thereby reducing theangles through which the plates 184 must rotate.

As illustrated in FIG. 13, all electrical connections to the torsionalscanners 172 occur at the frontside 169 of the device silicon layer 166,and as illustrated in FIG. 15 the beam of light 108 reflects off ametallic layer coated onto the backside 170 of the device silicon layer166. To form electrical connections between the substrate 212 and thetorsional scanners 172 in the strip 222, the strip 222 is preferablyflip-chip bonded to the substrate 212. The substrate 212 may accommodatemore than one strip 222 by using a substrate 212 that is larger than thestrip 222. The substrate 212 may be fabricated in various differentways.

Preferably, the substrate 212 is fabricated from a ceramic material suchas aluminum oxide (alumina), or, to more closely match the coefficientof thermal expansion of silicon, aluminum nitride. To provide highdensity electrical interconnections for coupling the torsional scanners172 with the ribbon cable 226, electrically conductive vias are laserdrilled or punched through ceramic material forming the substrate 212.

Alternatively, the substrate 212 may be fabricated from a 100 wafer ofsilicon. If the substrate 212 is fabricated from a silicon wafer, thencavities 272 may be anisotropically etched into the substrate 212 toprovide space for rotation of the plates 184, and to establish aprecisely controlled spacing between the plate 184 and electrodes 214located in the cavities 272. Electrical insulation between leads 228 andbetween electrodes 214 may be obtained by forming an electricallyinsulating oxide on the surface of the silicon substrate 212. Theelectrodes 214 may either be integrated into the silicon substrate 212or deposited onto the silicon surfaces within each of the cavities 272.

If the substrate 212 is fabricated from a silicon wafer, then electroniccircuits may also be advantageously integrated thereinto. The circuitsincluded in a silicon substrate 212 may include current sources forproviding an electrical current to the torsion sensors 192 a and 192 bof the torsional scanners 172, differential amplifiers for receivingsignals from the torsion sensors 192 a and 192 b which indicate theorientation of the inner moving frame 178 and the plate 184, andamplifiers for supplying high voltage signals to the electrodes 214 thatenergize rotation of the plate 184. Incorporating these variousdifferent type of electronic circuits into the substrate 212significantly reduces the number of leads that must be included in theribbon cable 226. The number of leads in the ribbon cable 226 may beeven further reduced by including one or more multiplexer circuits inthe silicon substrate 212.

Photo-detectors which respond to a wavelength of light present in thebeam of light 108 and which are disposed on the surface of the substrate212 adjacent to the strip 222 outside shadows cast by the mirrorsurfaces 116 may be advantageously included on the substrate 212 todetect if a portion of the beam of light 108 misses the mirror surfaces116. For wavelengths of light used for optical fiber telecommunications,such photo-detectors sense if a portion of the beam of light 108 missesthe mirror surfaces 116 even if they are covered by portions of thestrip 222 other than the mirror surfaces 116 because silicon istransparent to light at wavelengths used for optical fibertelecommunications.

Referring now to FIGS. 22a-22 c, the strip 222 is joined to thesubstrate 212 by electrically-conductive bonds 276 formed in variousways to be described in greater detail below. Theelectrically-conductive bonds 276 rigidly interconnect pads on thesubstrate 212 with the pads 194, 198 and 202 of the torsional scanners172 of the strip 222. The flip-chip bonding of materials forming thestrip 222 and the substrate 212 which have closely matched coefficientsof thermal expansion introduces a negligible amount of stress therebykeeping the strip 222 flat.

The electrically-conductive bonds 276 can be made out of solder,electroplated metal and/or electrically conductive epoxy material.Electrically conductive epoxy provides a compliant connection for theelectrically-conductive bonds 276 that absorbs mismatch in coefficientsof thermal expansion between the strip 222 and the substrate 212 thusreducing stress on the strip 222. Conductive epoxy material can bescreen printed, or dispensed from a syringe. Projecting Au stud bumps orelectroplated metal bumps may be formed at appropriate locations on thestrip 222 and/or on the substrate 212 in conjunction with electricallyconductive epoxy material to provide:

1. improved connections between the strip 222 and the substrate 212; and

2. greater thermal conductivity between the strip 222 and the substrate212.

The Au stud bumps can be coined to ensure that they have a uniformheight, and/or to shape them for increasing mechanical bond strengthwith the epoxy.

Electrically conductive epoxy material usually bonds well to substrates212 formed using ceramic material such as aluminum oxide or aluminumnitride. However, the electrically conductive epoxy material does notform a similarly strong a bond with the strip 222. The cross-sectionaldiagram of FIG. 22e illustrates roughening the surface of contact padson the strip 222 by anisotropically etching truncated pyramidally-shapedtroughs 278 into the device silicon layer 166 of the wafer 162. Thetroughs 278 increases the surface bonding area between theelectrically-conductive bonds 276 and contact pads located at thetroughs 278 thereby anchoring the electrically-conductive bonds 276 moresecurely to the strip 222.

To increase the mechanical bond strength between the strip 222 and thesubstrate 212, to reduce thermomechanical stress on theelectrically-conductive bonds 276, and to protect theelectrically-conductive bonds 276 from environmental factors such ashumidity, any gap between peripheries of the strip 222 and the substrate212 can be eliminated by an underfill 279, illustrated in FIG. 22b. Toprevent entry of the underfill material into the cavities 272, a dammust surround them at least until the underfill 279 cures. A compliantunderfill 279 such as silicon can be used to absorb a coefficient ofthermal expansion mismatch between the substrate 212 and the strip 222thereby reducing stress on the strip 222.

If the substrate 212 is fabricated from silicon or from polysilicon,then as depicted in FIG. 22d a large number of very small electricallyconductive vias 282 may be formed, using a process similar to thatdescribed by Calmes, et al. in Transducers 99 at page 1500, through thesilicon wafer during fabrication of the substrate 212. Holes for thevias 282 are first formed through the wafer using the standard Boschdeep reactive ion etch (“RIE”) process. The holes may be 50 micron wideand 500 micron deep. The wafer is then oxidized thus establishing anelectrically insulating oxide layer 284 which isolates the hole from thesurrounding wafer. Then a highly doped polysilicon layer 286 is grownover the oxide layer 284 by providing a conductive path along thesurface of wafer and in the holes. Obtaining a sufficiently conductivepolysilicon layer may also require gas phase doping of the polysiliconlayer 286 with phosphorus. The conductive polysilicon layer 286 formedin this way electrically connects both sides of wafer. If desired, rings288 may then be etched through the polysilicon layer 286 around each via282 thereby electrically isolating the vias 282 from each other. Toincrease electrical conductivity of substrate 212 and to facilitateforming an electrical contact to the vias 282, one or more additionalmetal layers may be coated either on one or both sides of the substrate212 and appropriately patterned.

Mounting of the strip 222 to the substrate 212 that includes the vias282 is depicted in FIG. 22d. Electrical connections between the strip222 and vias 282 of the substrate 212 are again formed byelectrically-conductive bonds 276. An elastomer layer 292 fastens apolyimide and copper sheet 294 which forms the ribbon cable 226 to theside of the substrate 212 furthest from the strip 222 of torsionalscanners 172. Ballgrid or TAB bumps 298 make contact to the conductivevias 282 to establish electrical connections with the polyimide andcopper sheet 294. In this way a very large number of contacts to bebrought through the substrate 212 with relatively low electricalresistance vias 282.

If the substrate 212 is fabricated from polysilicon or from Pyrex glass,then the cavities 272 may be etched thereinto. However, if the substrate212 is made from a ceramic material or Pyrex then the electrodes 214must be deposited onto surfaces within the cavities 272. If the strip222 is fabricated from a flat sheet of material such as ceramic, then asillustrated in FIG. 22f a layer of material providing a spacer 299 mustbe inserted between the strip 222 and the substrate 212. For substrates212 lacking etched cavities 272, the spacer 299 establishes a preciselycontrolled gap between the plates 184 and the electrodes 214 thatpermits rotation of the plates 184. The spacer 299 may be arranged toalso provide a dam that bars entry of the underfill 279 into thecavities 272. The spacer 299 may be made by screen printing materialonto the substrate 212 which is subsequently lapped to the appropriatethickness. Preferably, the spacer 299 is made using either a solder dammaterial Vacrel® manufactured by E. I. du Pont de Nemours and Company,or a dry film photoresist material that is laminated onto the substrate212 and photolithographically patterned. Several layers of dry filmmaterial of the same or differing thicknesses can be stacked to providethe desired thickness for the spacer 299. If the dry film acts as anegative, a sequence of films can be stacked and exposed withoutdevelopment after each lamination thereby assembling a pyramidal-shapedstructure. With the spacer 299 secured to the substrate 212, a syringecan be used to dispense conductive epoxy material for theelectrically-conductive bonds 276, and the conductive epoxy materialneed not be cured or b-staged before juxtaposing the substrate 212 withthe strip 222. The spacer 299 thus established between the substrate 212and the strip 222 also mechanically isolates adjacent torsional scanners172.

Note that steep sides 302 formed by 111 planes exposed by anisotropicetching of the handle silicon layer 168 of the wafer 162, illustrated inFIG. 15, prove very advantageous for flip-chip bonding. Not only do thesides 302 substantially protect the mirror surface 116 on the backside170 of the plate 184 from damage during manufacturing while concurrentlymechanically reinforcing the strip 222, but their steep angle scarcelyobscures the beam of light 108 impinging upon the mirror surface 116 atan angle of approximately 45°. Furthermore, the mirror surface 116 maybe protected from contamination by stretching an extremely thin pellicle304, similar to those used for integrated circuit (“IC”) masks, acrossthe backside of the handle silicon layer 168.

Due to the presence of the handle silicon layer 168 surrounding themirror surface 116, the flip-chip configuration for mounting thetorsional scanner 172 also permits advantageously reducing lightscattering as illustrated in FIG. 23. The steep sides 302 andsurrounding backside of the handle silicon layer 168 may be coated withan anti reflection layer 312 which effectively absorbs stray lightimpinging thereon as the beam of light 108 switches between mirrorsurfaces 116. The steep sides 302 also scatter stray light from the beamof light 108 at very large angles which prevents the side 102 a or 102 btoward which the beam of light 108 propagates from receiving stray lightas the beam of light 108 switches between mirror surfaces 116.

FIG. 24 schematically illustrates the reflective switching module 100,such as those illustrated in FIGS. 2, 4 a-4 b, 5, 6 and 7 as describedthus far, encased within an environmental housing 352 that completelyencloses the optical path through which the beams of light 108propagate. As described above, the reflective switching module 100mechanically interconnects the sides 102 a and 102 b and the sets 118 aand 118 b and keeps them rigidly aligned. The environmentally sealedenvironmental housing 352, which protects the reflective switchingmodule 100, may provide temperature regulation thereby maintaining astable operating environment for the reflective switching module 100. Acontrolled, dry gas, such as nitrogen, may flow through theenvironmental housing 352 to hinder moisture from condensing within thereflective switching module 100. The environmental housing 352 may alsobe slightly pressurized to exclude the surrounding atmosphere from thereflective switching module 100. The environmental housing 352 mayinclude a nonsaturable microdryer 353 as described in U.S. Pat. No.4,528,078 to control the humidity of atmosphere within the reflectiveswitching module 100. A wall 354 of the environmental housing 352 ispierced by electrical feed-throughs 356 for ribbon cables 226. Theoptical fiber collimator assemblies 134 secured about the ends 104 ofthe optical fibers 106 plug directly into the convergence blocks 152which project through the environmental housing 352. In this way, theenvironmental housing 352 almost hermetically encloses the reflectiveswitching module 100. Within the environmental housing 352, to reducethe possibility of optical misalignment, the ribbon cables 226 arerouted carefully to avoid applying stresses to the reflective switchingmodule 100, particularly the support frames 224 and the substrates 212.

Fiber Optic Switch

FIG. 25 illustrates a modular fiber optic switch in accordance with thepresent invention referred to by the general reference character 400.The fiber optic switch 400 includes a standard twenty-three (23) inchwide telecommunications rack 402 at the base of which is located theenvironmental housing 352 containing the reflective switching module100. The environmental housing 352 containing all the torsional scanners172 rests on a special pedestal on the floor immediately beneath therack 402, and is only very flexibly connected to the rack 402.Supporting the environmental housing 352 on the special pedestalminimizes vibration, etc. and thermally couples the environmentalhousing 352 to the floor to enhance its thermal regulation.

Portcard

Mounted in the rack 402 above the environmental housing 352 are numerousduplex sockets 404 included in portcards 406 that are adapted to receiveduplex pairs of optical fibers 106. One optical fiber 106 of a duplexpair brings one beam of light 108 to the fiber optic switch 400 andanother receives one beam of light 108 from the fiber optic switch 400.The portcards 406 are arranged either horizontally or vertically withinthe rack 402, and can be individually removed or installed withoutinterfering with immediately adjacent portcards 406. As is a commonpractice in the telecommunications industry, the portcards 406 are hotswappable. The reflective switching module 100 may contain spare mirrorsurfaces 116 so the fiber optic switch 400 can retain its full operatingcapability if a few of the mirror surfaces 116 were to fail. It isreadily apparent that, in principle, all or any lesser number of theoptical fibers 106 connected to a portcard 406 may receive a beam oflight 108 therefrom. Similarly, all or any lesser number of the opticalfibers 106 connected to a portcard 406 may carry a beam of light 108 tothe portcard 406. The optical fibers 106 may be organized in duplexpairs as illustrated in FIG. 26, but need not be so organized.

In the block diagram of FIG. 26, all items to the left of a dashed line412 are included in the portcard 406, and all items to the right of adashed line 414 are included in the reflective switching module 100. Thearea between the dashed lines 412 and 414 illustrates a backplane of therack 402. Each portcard 406 includes electronics, alignment optics andelectro-optics required to control operation of a portion of thereflective switching module 100. Thus, all of the optical fibers 106included in the reflective switching module 100 connect to a portcard406. Similarly, all of the torsional scanners 172 having mirror surfaces116 upon which any of the beams of light 108 may impinge connect via itssubstrate 212 and a ribbon cable 226 to a portcard 406. Each portcard406 preferably, but not necessarily, connects to sixteen (16) orthirty-two (32) optical fibers 106, one-half of which it is envisionedmay be receiving a beam of light 108 from the portcard 406 and one-halfthat may be carrying a beam of light 108 to the portcard 406. In FIG. 26the odd number subscripted optical fibers 106 ₁, 106 ₃, . . . 106_(2n−1) carry a beam of light 108 to the reflective switching module 100while the even number subscripted optical fibers 106 ₂, 106 ₄, . . . 106_(2n) carry a beam of light 108 from the reflective switching module100.

The portcard 406 includes light sources 422 and taps or directionalcouplers 424 for supplying and coupling light into the optical fiber 106for use in servo alignment of the reflective switching module 100. Thedirectional couplers 424 also supply light received from the reflectiveswitching module 100 via optical fibers 106 to light detectors 426. Theportcard 406 also includes driving, sensing and control electronics 432,e.g. a digital signal processor (“DSP”) together with its associatedcircuits, which exchange electrical signals via the ribbon cables 226with the electrodes 214 included in the substrates 212 and with thetorsion sensors 192 a and 192 b included in each of the torsionalscanners 172 mounted on the substrates 212. The driving, sensing andcontrol electronics 432 controls the orientation of mirror surfaces 116including implementing servo loops that ensure their proper orientation,and also communicates with the supervisory processor 436 through anRS232 data communication link 438.

The backplane between dashed lines 412 and 414 includes connections forthe optical fibers 106 to the portcards 406, preferably multifiberconnectors for single mode, optical fiber ribbon cables that connect,for example, 12, 16 or more optical fibers 106. The backplane betweendashed lines 412 and 414 also includes connectors 442 for all the ribboncables 226, the data communication link 438 and other miscellaneouselectrical connections such as electrical power required for operationof the driving, sensing and control electronics 432.

In orienting a pair of mirror surfaces 116, one in each of the sets 118a and 118 b, to couple one beam of light 108 between one optical fiber106 at side 102 a and another at side 102 b, the two mirror surfaces 116are initially oriented appropriately using pre-established angularcoordinates which specify rotations about two (2) axes for each mirrorsurface 116 in the pair. Thus, for an N×N reflective switching module100 and ignoring any spare mirror surfaces 116 included in thereflective switching module 100, the fiber optic switch 400 must store4×N² values for orientation signals produced by the torsion sensors 192a and 192 b included in each torsional scanner 172. Accordingly, thereflective switching module 100 includes a look-up table 452,illustrated in FIG. 27a that is maintained in the supervisory processor436, that stores the 4×N² values for orientation signals for use at anytime during the operating life of the fiber optic switch 400.

The 4×N² values for orientation signals produced by the torsion sensors192 a and 192 b included in each torsional scanner 172 may be initiallydetermined analytically. During assembly of the fiber optic switch 400,the analytically determined coordinates and orientation signals are finetuned to accommodate manufacturing tolerances, etc. Furthermore,throughout the operating life of the fiber optic switch 400 thesecoordinates and orientation signals may be updated when necessary.Accordingly, the look-up table 452 stores compensation data for initialvalues of the coordinates and orientation signals, e.g. sensor offsetsand temperature compensation since the temperature coefficient of thetorsion sensors 192 a and 192 b is well characterized.

In a preferred embodiment of the fiber optic switch 400, a higherfrequency servo system uses the orientation signals produced by thetorsion sensors 192 a and 192 b in controlling orientation of eachmirror surface 116. The frequency response of this higher frequencyservo system permits accurate orientation of pairs of mirror surfaces116 when switching from one pairing of optical fibers 106 to anotherpairing. The higher frequency servo system also maintains orientation ofall mirror surfaces 116 despite mechanical shock and vibration. Toensure precise orientation of pairs of mirror surfaces 116 duringoperation of the fiber optic switch 400, the fiber optic switch 400 alsoemploys lower frequency optical feedback servo described in greaterdetail below.

In initially orienting a pair of mirror surfaces 116, one in each of thesets 118 a and 118 b, to couple one beam of light 108 between oneoptical fiber 106 at side 102 a and another at side 102 b, stored valuesfor orientation signals are transmitted from the look-up table 452respectively to two dual axis servos 454 that are included in theportcards 406 for each torsional scanner 172 which exchanges signalswith the portcard 406. Each dual axis servo 454 transmits drivingsignals via the ribbon cable 226 to the electrodes 214 included in thesubstrates 2i2 to rotate the mirror surfaces 116 to pre-establishedorientations. The two torsion sensors 192 a and 192 b included in eachtorsional scanner 172 transmit their respective orientation signals backto the respective dual axis servos 454 via the ribbon cable 226. Thedual axis servos 454 respectively compare the orientation signalsreceived from their associated torsion sensors 192 a and 192 b with thevalues for orientation signals received from the look-up table 452. Ifany difference exists between the stored values for orientation signalsreceived from the look-up table 452 and the orientation signals whichthe dual axis servos 454 receive from their respective torsion sensors192 a and 192 b, then the dual axis servos 454 appropriately correct thedriving signals which they transmit to the electrodes 214 to reduce anysuch difference.

FIG. 27b depicts one of two identical channels, either x-axis or y-axis,of the dual axis servos 454. As depicted in that FIG. and as describedabove, a current source 462, included in the portcard 406, supplies anelectric current to the series connected torsion sensors 192 a and 192 bof the torsional scanner 172. Differential output signals from one orthe other of the torsion sensors 192 a and 192 b, in the illustration ofFIG. 27 the X-axis torsion sensor 192 b, are supplied in parallel viathe ribbon cable 226 to inputs of an instrumentation amplifier 463 alsoincluded in the portcard 406. The instrumentation amplifier 463transmits an output signal that is proportional to the signal producedby the X-axis torsion sensor 192 b to an input of an error amplifier464.

As described above, the driving, sensing and control electronics 432 ofthe portcard 406 includes a DSP 465 which executes a computer programstored in a random access memory (“RAM”) 466. Also stored in the RAM 466are values for orientation signals which specify an orientation for themirror surface 116 that have been supplied from the look-up table 452maintained at the supervisory processor 436. The computer programexecuted by the DSP 465 retrieves the angular coordinate, either X-axisor Y-axis as appropriate, and transmits it to a digital-to-analogconverter (DAC) 467. The DAC 467 converts the angular coordinatereceived from the DSP 465 in the form of digital data into an analogsignal which the DAC 467 transmits to an input of the error amplifier464.

An output of the error amplifier 464 transmits a signal to an input ofan integrator circuit 472 that is proportional to the difference betweenthe analog signal representing the angular coordinate and the signalfrom the instrumentation amplifier 463 that is proportional to thesignal produced by the X-axis torsion sensor 192 b. The integratorcircuit 472, consisting of an amplifier 473 and a network of resistors474 and capacitors 475, transmits an output signal directly to an inputof a summing amplifier 476 a, and to an input of an inverting amplifier477. The inverting amplifier 477 transmits an output signal to an inputof a second summing amplifier 476 b. In addition to the signalsrespectively received directly from the integrator circuit 472 andindirectly from the integrator circuit 472 via the inverting amplifier477, inputs of the summing amplifiers 476 a and 476 b also receive afixed bias voltage. The summing amplifiers 476 a and 476 b respectivelytransmit output signals, which are proportional to a sum of theirrespective input signals, to inputs of a pair of high voltage amplifiers478 a and 478 b. The high voltage amplifiers 478 a and 478 brespectively transmit driving signals via the ribbon cable 226 either tothe X-axis or to Y-axis electrodes 214 of the torsional scanner 172.

In this way the dual axis servos 454 supply differential drive signalsto the electrodes 214 of the torsional scanner 172 which respectivelyare symmetrically greater than and less than a voltage established bythe bias voltage supplied to the summing amplifiers 476 a and 476 b.Furthermore, the drive signals which the dual axis servos 454 supply tothe electrodes 214 are appropriately corrected to reduce any differencethat might exist between the output signals from the torsion sensors 192a and 192 b and the values for orientation signals specified in thelook-up table 452.

Since single crystal silicon at room temperatures does not undergoplastic deformation, is dislocation free, has no losses, and does notexhibit fatigue, the mechanical characteristics of torsional flexurehinges 176 and torsion-bar hinge 182 made from that material remainstable for years. Consequently, a combination of the long term stabilityof the torsional flexure hinges 176 and torsion-bar hinge 182 and thetorsion sensors 192 a and 192 b assure that the values for orientationsignals which the look-up table 452 supplies to the pair of dual axisservos 454 will effect almost precise alignment of pairs of mirrorsurfaces 116.

However, as is disclosed in the '463 and the '153 patents, inclusion ofan optical servo loop in a fiber optic switch ensures precise alignment.To permit implementing such an optical servo loop, as depicted in FIG.26 each portcard 406 included in the fiber optic switch 400 includes onedirectional coupler 424 for each optical fiber 106 together with onelight detector 426. Each directional coupler 424 couples approximately5% to 10% of light propagating through one optical fiber included in thedirectional coupler 424 into another optical fiber with 95% to 90% ofthat light remaining in the original optical fiber. Consequently, if alight source 422 is turned-on 5% to 10% of the light emitted by thelight source 422 into the directional coupler 424 passes into anincoming optical fiber 106, e.g. optical fiber 106 ₁, for transmissiononto the reflective switching module 100 together with 95% to 90% of anyother light that is already propagating along the optical fiber 106toward the reflective switching module 100. The reflective switchingmodule 100 couples this combined light from the incoming optical 106 ₁,fiber 106, e.g. optical fiber 106 ₁, into an outgoing optical fiber 106,e.g. optical fiber 106 ₂. Upon reaching the directional coupler 424associated with the outgoing optical fiber 106, e.g. optical fiber 106₂, 5% to 10% of the light received from the reflective switching module100 passes from the optical fiber 106 through the directional coupler424 to the light detector 426 connected to that directional coupler 424.If necessary, the fiber optic switch 400 exploits the ability tointroduce light into the optical fiber 106 for transmission through thereflective switching module 100 and then recovering a fraction of thetransmitted light to analyze and adjust the initial operating state ofspecific pairs of mirror surfaces 116.

In considering operation of this optical servo portion of the fiberoptic switch 400, it is important to note that the optical servo alignsa pair of mirror surfaces 116 regardless of the direction in whichalignment light propagates through the pair of mirror surfaces 116, i.e.from incoming optical fiber 106 to outgoing optical fiber 106 orconversely. Consequently, in principle the portcards 406 need equip onlyone-half of the optical fibers 106 included in the fiber optic switch400, e.g. all the incoming optical fibers 106 or all the outgoingoptical fibers 106, with the light source 422. However, to facilitateflexible and reliable operation of the fiber optic switch 400 in atelecommunication system all of the directional couplers 424, both thoseconnected to incoming and to outgoing optical fibers 106, may, in fact,be equipped with the light source 422.

When initially aligning pairs of mirror surfaces 116, if the the fiberoptic switch 400 detects sufficient light propagating along an incomingoptical fiber 106, it will use the incoming light for alignment.However, if there is insufficient light propagating along the incomingoptical fiber 106, then light from the light source 422 coupled into theoptical fiber 106 is intensity modulated at a very low frequency, e.g.turned on and off, and the signal produced by light detectors 426analyzed to detect the presence of the modulation on outgoing opticalfibers 106. If light from the light source 422 is used for alignment,the portcard 406 through which the outgoing optical fiber 106 passesprevents the intensity modulated light from leaving the fiber opticswitch 400. The light on the outgoing optical fiber 106 may be keptwithin the fiber optic switch 400 by including a 1×2 switch at theoutput of the portcard 406 and directing the modulated light generatedby the light source 422 to a dead-ended optical fiber. By modulating thelight produced by different light sources 422 in differing ways, e.g. atdifferent frequencies or in differing patterns, the reflective switchingmodule 100 can concurrently perform initial alignment of many differentpairs of mirror surfaces 116 coupling beams of light 108 between pairsof ends 104, and may verify the existence of a specified correctconnection.

Referring now to FIG. 26a, an output from every directional coupler 424of the portcard 406 supplies light to a telecom-signal-strengthphoto-detector 482. Every telecom-signal-strength photo-detector 482receives and responds to a fraction of light propagating into thereflective switching module 100 along the optical fibers 106 regardlessof whether the optical fiber 106 is an incoming or an outgoing opticalfiber 106. Thus, after a pair of mirror surfaces 116 have been initiallyaligned, perhaps using intensity modulated light from the light source422, output signals from two telecom-signal-strength photo-detectors 482indicate whether portcard 406 must supply light from the light source422 for precisely aligning the mirror surfaces 116 or whether theincoming optical fiber 106 carries a telecommunication signal ofsufficient strength to permit precise optical alignment. If the signalsfrom the pair of telecom-signal-strength photo-detectors 482 indicatethat neither of two optical fibers 106 carry sufficient light to performprecise optical alignment, then the portcard 406 turns-on the lightsource 422 to obtain the required light, otherwise light present on anincoming optical fiber 106 is used for that purpose.

One approach for using light introduced into the optical fiber 106 fromthe light source 422 illustrated in FIG. 26a envisions using 850 nmlight from a relatively inexpensive laser diode for the light source422. In this approach, an alignment-light detector 484 that is sensitiveto red wavelengths of light may be an inexpensive siliconphoto-detector. However, in addition to light generated by the lightsource 422 at 850 nm, the incoming optical fiber 106 may also beconcurrently carrying light at optical telecommunication wavelengths,e.g. 1310 A° or 1550 A°, which perhaps has greater power than thatgenerated by the light source 422. To ensure separation of the 850 nmalignment light generated by the light source 422 _(2j−1) and suppliedto the reflective switching module 100 via optical fiber 106 _(2j−1)from light at optical telecommunication wavelengths, the output of thedirectional coupler 424 which emits a portion of the light received bythe portcard 406 from the reflective switching module 100 directs suchlight onto a dichroic mirror 486 _(2j). The dichroic mirror 486 _(2j)reflects the 850 nm alignment light to the alignment-light detector 484while permitting light at optical telecommunication wavelengths to passonto a telecom-signal-monitoring photo-detector 488. If the reflectiveswitching module 100 is to be fully bidirectional so any optical fiber106 may at any instant be an incoming or an outgoing optical fiber 106,then a dichroic mirror 486 _(2j−a) must be used with the directionalcoupler 424 _(2j−1) to separate light from the light source 422 _(2j−1)from light at optical telecommunication wavelengths that thetelecom-signal-monitoring photo-detector 488 _(2j−1) receives.

For several reasons after the pair of mirror surfaces 116 have beeninitially precisely aligned optically to establish a connection via thereflective switching module 100 between an incoming optical fiber 106and an outgoing optical fiber 106, it appears advantageous to turn-offthe light source 422 and to use light coming to the fiber optic switch400 at optical telecommunication wavelengths in periodically checkingalignment. The configuration of the light source 422 and light detector426 remains as depicted in FIG. 26a. operating in this way, thetelecom-signal-strength photo-detector 482 which first receives light atoptical telecommunication wavelengths coming into the fiber optic switch400 via the duplex sockets 404 detects loss of light or loss ofmodulation in incoming light. During such operation of the fiber opticswitch 400, the telecom-signal-monitoring photo-detectors 488 are usedin conjunction with the telecom-signal-strength photo-detectors 482 forperiodically monitoring and maintaining the quality of lighttransmission through the reflective switching module 100. Tests havedemonstrated that the orientation signals from the torsion sensors 192 aand 192 b supplied to the dual axis servo 454 maintain adequatealignment of the mirror surfaces 116 for extended period of time, e.g.hours. Consequently, after a pair of mirror surfaces 116 have beenprecisely aligned optically only relatively infrequent adjustment of themirror orientation is required to compensate for drift in the torsionsensors 192 a and 192 b, temperature changes, mechanical creep of thereflective switching module 100 including the support frames 224 andperhaps the substrates 212, etc.

In an alternative approach for detecting alignment light supplied fromthe light source 422 at 850 nm, the dichroic mirror 486 _(2j) and itsassociated photo-detectors 484 and 488 may be replaced by a compoundsandwich photo-detector, illustrated in FIG. 26b. In the compoundsandwich detector illustrated there, a silicon photo-detector 492 ismounted over a long wavelength photo-detector 494 such as germanium (Ge)or indium gallium arsenide (InGaAs) photo-detector. The compoundsandwich photodetector absorbs the shorter alignment wavelength in thesilicon photo-detector 492. However, longer wavelengths of the opticaltelecommunications light pass virtually un-attenuated through thesilicon photo-detector 492 to be absorbed in the long wavelengthphoto-detector 494. Use of the compound sandwich photo-detector fullyseparates the two signals. The InGaAs photo-detector may be replaced bya second Ge photo-detector to detect the longer wavelength light, butwith less sensitivity than the InGaAs photo-detector. However, adifficulty associated with using light at 850 nm for alignment is thatthe directional couplers 424 become multi-mode devices so the fractionof the alignment light being coupled into and out of the optical fiber106 varies over time.

To avoid difficulties associated with using 850 nm light for preciselyaligning a pair of mirror surfaces 116 optically, it is also possibleand advisable to supply light at optical telecommunication wavelengths,e.g. 1310 A° or 1550 A°, from the light source 422. Light at thesewavelengths may be provided by an inexpensive vcsel. While vcsels lackthe precise wavelength or stability of expensive laser sources of suchlight, the precision and stability provided by laser sources are notrequired for optically aligning a pair of mirror surfaces 116. Usinglight at optical telecommunication wavelengths has the advantage thatthe and the alignment-light detector 484 may be eliminated, and that thecoupling coefficient for the directional couplers 424 are higher andmore stable than for 850 nm light. Therefore, a vcsel need supply lesslight or power for optical alignment than a laser diode producing 850 nmlight.

Because every optical fiber 106 passes through a portcard 406, asignificant portion of the manufacturing cost of the fiber optic switch400 is the cost of the portcards 406. Thus, it is economicallyadvantageous to reduce, as much as practicable, the manufacturing costfor portcards 406. Thus, if initial optical alignment of pairs of mirrorsurfaces 116 requires using an expensive laser that generates light atoptical telecommunication wavelengths for the light source 422, the costof that source may be shared among directional couplers 424 using a 1×Noptical switch. Such a 1×N optical switch may be very large to providelight to all the portcards 406. Alternatively, to enhance reliabilitythe fiber optic switch 400 might include several such opticaltelecommunication lasers with a smaller 1×N optical switches each one ofwhich provides light to only the directional couplers 424 included in asingle portcard 406.

As described thus far, the portcards 406 use directional couplers 424 toinject light into or extract light from the optical fibers 106. Sincedirectional couplers 424 are a comparatively expensive component,reducing their cost is advantageous. FIGS. 26c and 26 d illustrate usinglower cost, bent-fiber taps 495 for injecting light into or extractinglight from the optical fibers 106 as is commonly done when fusingoptical fibers.

In the illustration of FIG. 26c, each incoming optical fiber 106 _(2j−1)bends around a sufficiently small, grooved mandrel 496 so light radiatesfrom the optical fiber 106 _(2j−1) as is well known in the art. Thistechnique also permits injecting light emitted from the light source 422into the core or cladding of the optical fiber 106 _(2j−1) although thatis less desirable because the cladding permits multi-mode lightpropagation. Light propagating in the core of the optical fiber 106_(2j−1) then becomes the beam of light 108 that is directed by a pair ofmirror surfaces 116 to the output optical fiber 106 _(2j). Each outgoingoptical fiber 106 _(2j) also bends around a mandrel 496 so lightradiating from the optical fiber 106 _(2j) strikes the light detector426 _(2j). The light detector 426 _(2j) may have two (2) sections 426 aand 426 b, one section 426 a for monitoring alignment light, and onesection 426 b for monitoring light at optical communication wavelengths.Alternatively, the light detector 426 _(2j) may be of the typeillustrated in FIG. 26b and described previously in which the sections426 a and 426 b overlay each other.

As described previously, the telecom-signal-strength photo-detector 482_(2j−1) monitors loss and loss of modulation of optical communicationlight propagating into the reflective switching module 100 along theinput optical fiber 106 _(2j−1), while the section 426 b _(2j) monitorslight that passes through the reflective switching module 100 at opticalcommunication wavelengths. The telecom-signal-strength photo-detector482 _(2j) and light detector 426 _(2j−1) serve the correspondingfunctions for bi-directional duplex optical fibers 106.

If alignment light has the same wavelength as optical communicationlight, then using tandem detection is unnecessary. As describedpreviously, in principle the same light source 422 may inject light intoseveral optical fibers 106 simultaneously. Alignment light may becoupled into the cladding or into the core of the optical fiber 106_(2j−1). If coupled into the cladding, the alignment light may beremoved from the optical fiber 106 _(2j) by an absorber 497 locatedalong the output optical fiber 106 _(2j) past the mandrel 496. This thenallows continuous use of virtually any wavelength of light for aligningthe mirror surfaces 116, since no alignment light propagates beyond theportcard 406. The bent-fiber tap 495 may be employed for all opticalfibers 106, both incoming and outgoing of the portcard 406.

Other possibilities exist for reducing the cost of the portcards 406.For example, because the plates 184 carrying the mirror surfaces 116move comparatively slowly in comparison with digital electronic signals,and because the electrodes 214 and the plates 184 form a capacitor thatwill, for a short interval, store an applied voltage, most circuitry ofthe dual axis servos 454 illustrated in FIG. 27b may be time-sharedamong several different pairs of electrodes 214. FIG. 27c illustrates acircuit for sharing a single channel of one dual axis servo 454 amongseveral different pairs of electrodes 214. In the illustration of FIG.27c, the output signal from the high voltage amplifiers 478 a and 478 bare supplied respectively to inputs of high-voltage multiplexers 512 aand 512 b. Other inputs of the high-voltage multiplexers 512 a and 512 breceive digital selection signals sent from the DSP 465 via a set ofdigital control lines 514. Output signal lines from the high-voltagemultiplexers 512 a and 512 b connect respectively to individualelectrodes 214, for example all the electrodes 214 that connect to asingle portcard 406.

The digital selection signals supplied to the high-voltage multiplexers512 a and 512 b specify to which of several pairs of electrodes 214 thevoltages present at the outputs of the high voltage amplifiers 478 a and478 b are respectively applied by the high-voltage multiplexers 512 aand 512 b. When a particular pair of electrodes 214 is to be selected,in addition to transmitting the appropriate digital selection signals tothe high-voltage multiplexers 512 a and 512 b, the DSP 465 alsotransmits data specifying the appropriate output voltages to the DAC467. Responsive to the data received by the DAC 467, the high voltageamplifiers 478 a and 478 b then produce appropriate driving voltages forthe selected pair of electrodes 214 while the high-voltage multiplexers512 a and 512 b couple that voltage to electrodes 214 selected.

If the capacitance provided by pairs of electrodes 214 and theirassociated plate 184 is insufficiently large to adequately store anapplied voltage throughout the interval between successive connectionsbetween the electrodes 214 and the high voltage amplifiers 478 a and 478b via the high-voltage multiplexers 512 a and 512 b, then smallcapacitors 516 may be connected between the output signal lines of thehigh-voltage multiplexers 512 a and 512 b and circuit ground. Byswitching sufficiently rapidly, only a single pair of high voltageamplifiers 478 a and 478 b are needed for all the electrodes 214connected to the portcard 406. The digital computer program executed bythe DSP 465 may select pairs of electrodes 214 in a sequence thatminimizes the change in voltage which the high voltage amplifiers 478 aand 478 b must supply to successive pairs of electrodes 214 therebyreducing the slewing requirement of the high voltage amplifiers 478 aand 478 b.

Alternatively, because the electrostatic force between the plate 184 anda pair of electrodes 214 is independent of the sign of the appliedvoltage, rotation of the plate 184 can be induced by an alternatingcurrent (“AC”) voltage rather than a direct current (“DC”) voltage.Moreover, an AC driving voltage can be applied between the plate 184 anda pair of electrodes 214 using step-up transformers. The use of suchstep-up transformers simplifies the circuit which applies the drivingsignal to the electrodes 214 because the primary of the transformerreceives a much lower voltage that is more compatible with semiconductordevices thereby eliminating any need for high voltage components.

FIG. 27d depicts a circuit for applying an AC voltage to the electrodes214 of a torsional scanner 172 to induce rotation both of the plate 184and of the inner moving frame 178. The circuit illustrated in FIG. 27dincludes three (3) high-frequency transformers 522, 524 and 526 each ofwhich preferably has a ferrite core. An oscillator 528 supplies a low ACvoltage, e.g. 10 volts peak-to-peak (“P-P”), to a primary winding 532 ofthe transformer 522 at a high frequency, i.e. significantly higher thanthe mechanical resonant frequency of the plate 184. The transformer 522increases the AC voltage received from the oscillator 528 twenty (20)times to approximately 200 volts P-P at an secondary winding 534 of thetransformer 522. The secondary winding 534 of the transformer 522connects respectively to center taps of secondary windings 536 a and 536b of the transformers 524 and 526. Opposite terminals of the secondarywinding 536 a of the transformer 524 connect to the electrodes 214 a and214 b that are juxtaposed with the plate 184. Similarly, oppositeterminals of the secondary winding 536 b of the transformer 526 connectto the electrodes 214 a and 214 b that are juxtaposed with the innermoving frame 178.

The low AC voltage supplied to the primary winding 532 of thetransformer 522 is also applied directly, and through an invertingamplifier 538, to inputs of multiplying DACs 542 a and 542 b. Similar tothe DAC 467 depicted in FIG. 27b, other inputs to the multiplying DACs542 a and 542 b receive angular coordinate data for the plate 184 andfor the inner moving frame 178 directly from the DSP 465. Outputs of themultiplying DACs 542 a and 542 b connect respectively to primarywindings 544 a and 544 b of the transformers 524 and 526. Connected inthis way to the transformers 524 and 526, the multiplying DACs 542 a and542 b can apply adjustable AC voltages to the primary windings 544 a and544 b of the transformers 524 and 526 that are either in-phase orout-of-phase with the AC voltage applied to the primary winding 532 ofthe transformer 522. The transformers 524 and 526 both increase the ACvoltage received respectively from the multiplying DACs 542 a and 542 bforty (40) times to approximately 400 volts P-P across the secondarywindings 536 a and 536 b. If the multiplying DACs 542 a and 542 b applyno voltage to the primary windings 544 a and 544 b of the transformers524 and 526, then no net torque is applied to the plate 184 or to theinner moving frame 178.

FIG. 27e illustrates waveforms at the secondary winding 534 of thetransformer 522 and respectively at the electrodes 214 a and 214 b thatare juxtaposed with the plate 184 when, responsive to data received fromthe DSP 465, the multiplying DAC 542 a applies an AC voltage across thetransformer 524 in-phase with the voltage applied to the primary winding532 of the transformer 522. Because the electrostatic force between theplate 184 and a pair of electrodes 214 is independent of the sign of theapplied voltage, for the waveforms depicted in FIG. 27e the forcesapplied to the plate 184 respectively by the electrodes 214 a and 214 bdiffer. Not only can the multiplying DACs 542 a and 542 b apply unequal,in-phase AC voltages across the primary windings 544 a and 544 b of thetransformers 524 and 526 responsive to data received from the DSP 465,such data may also cause the multiplying DACs 542 a and 542 b to applyvoltages that are out-of-phase across the primary windings 544 a and 544b as indicated in FIG. 27f.

The net result of applying the voltages such as those illustrated eitherin FIG. 27e or in 27 f to the electrodes 214 is that the plate 184 tiltscloser to one of the electrodes 214 a or 214 b and away from the otherelectrode 214 b or 214 a. The inertia of the plate 184 smooths and evensout the effect of intermittent force applied at twice the frequency ofthe AC voltage produced by the oscillator 528. If the frequency of theAC voltage generated by the oscillator 528 is sufficiently low, then theresulting small oscillation of the plate 184 may be used for phasesensitive detection of signals for precisely aligning the beam of light108. Unequal forces may also be applied to the plate 184 by theelectrodes 214 a and 214 b by varying the phase relationship between aconstant amplitude AC voltage applied to the transformer 524 and thatapplied to the transformer 522, rather than by varying the AC voltageapplied to the transformer 524. Operation of the multiplying DAC 542 band the transformer 526 to effect rotation of the inner moving frame 178is identical to that described above for the plate 184.

Note that the dual axis servo 454 depicted in FIG. 27b applies symmetricDC voltages to pairs of electrodes 214 to induce rotation of the plate184 with the voltage on one electrode 214 increasing and the otherdecreasing by equal amounts. Such drive voltages balance any capacitivecoupling to the signals from the torsion sensors 192 a and 192 b becausethey are usually exposed symmetrically to the voltages applied to pairsof the electrodes 214. Furthermore, to minimize switching and transientnoise the long output lines from the torsion sensors 192 a and 192 b arearranged so that they are exposed equally to positive and negativevoltage swings. Techniques to balance the exposure of these signal linesto drive signals supplied to the electrodes 214 may include insertingadditional lines in connectors and/or leads, and applying voltages sothat each sensor line is fully symmetrically exposed to both voltageswings. Alternatively shielded lines may be used for signals from thetorsion sensors 192 a and 192 b, and the drive signal lines to theelectrodes 214 placed closely together to avoid inductive and capacitivecoupling.

Including the fiber optic switch 400 in a telecommunications networkmakes reliability and availability of utmost importance. Therefore, itis extremely important that the mirror surfaces 116 are always undercontrol of the dual axis servos 454, that initially forming a connectionwhich couples light from one optical fiber 106 to another optical fiber106 via the reflective switching module 100 be precise, and that thequality of the coupling be maintained while the connection persists. Asdescribed above in connection with FIGS. 26 and 26a, all the portcards406 provide a capability for monitoring the precise alignment of pairsof mirror surfaces 116 either with light incoming to the fiber opticswitch 400 or with light generated by one of the light sources 422.

The fiber optic switch 400 exploits the capability of the portcards 406to facilitate optical alignment of pairs of mirror surfaces 116 bymonitoring the quality of coupling between pairs of optical fibers 106connected to the reflective switching module 100. In monitoring thequality of that coupling, the fiber optic switch 400 tilts slightly eachmirror surface 116 in a pair from the orientation specified by thevalues for orientation signals stored in the look-up table 452, i.e.dithering both mirror surfaces 116, while concurrently monitoring thestrength of the beam of light 108 coupled between the two optical fibers106. Because, in general, monitoring the strength of the beam of light108 coupled between two optical fibers 106 requires coordination betweentwo of the at least thirty-six (36) portcards 406 included in the fiberoptic switch 400, that process must at least be supervised by thesupervisory processor 436 illustrated in FIG. 26. Accordingly, wheneverit is necessary or helpful to optically align a pair of mirror surfaces116 the supervisory processor 436 sends appropriate commands to the DSP465 included in each of the involved portcards 406, illustrated in FIG.27b, via the data communication link 438 and a RS232 port 502 includedin each of the portcards 406. The commands sent by the supervisoryprocessor 436 cause the DSP 465 to send coordinate data to the two DACs467 included in the dual axis servo 454 which tilts slightly the mirrorsurface 116 whose orientation the dual axis servo 454 controls. Becausethis change in orientation changes the impingement of the beam of light108 on the lens 112 associated with the outgoing optical fiber 106, theamount of light coupled into the associated optical fiber 106 changes.This change in the light coupled into the optical fiber 106 is coupledthrough the directional coupler 424 through which the outgoing lightpasses to the light detector 426 included in that portcard 406. Topermit detecting this change of light, the computer program executed bythe DSP 465 acquires light intensity data from an analog-to-digitalconverter (“ADC”) 504 that is coupled to the light detector 426 asillustrated in FIG. 27b. The fiber optic switch 400, either in the DSP465 on the portcard 406 or in the supervisory processor 436, or in both,analyzes this light intensity data to precisely align the two mirrorsurfaces 116 for coupling the beam of light 108 between the two opticalfibers 106.

After the mirror surfaces 116 have been precisely aligned optically, thefiber optic switch 400 confirms that light from the incoming opticalfiber 106 is being coupled through the reflective switching module 100to the proper outgoing optical fiber 106 by dithering only the mirrorsurface 116 upon which the incoming beam of light 108 first impinges. Ifthe reflective switching module 100 has been properly aligned to couplelight between a specified pair of optical fibers 106, the intensitymodulation of light from the incoming beam of light 108 caused bydithering this particular mirror surface 116 must appear in only thecorrect outgoing optical fiber 106, and in no other optical fiber 106.

After the pair of mirror surfaces 116 have been optically aligned asdescribed above, and after confirming that incoming light is beingcoupled through the reflective switching module 100 into the properoptical fiber 106, the fiber optic switch 400 periodically monitors thequality of the connection using the ability to dither the orientation ofthe mirror surfaces 116. The computer program executed by thesupervisory processor 436 as appropriate uses the alignment dataacquired in this way for updating the angular coordinate data stored inthe look-up table 452, and may also preserve a log of such data therebypermitting long term reliability analysis of fiber optic switch 400.

INDUSTRIAL APPLICABILITY

FIG. 28a shows an alternative embodiment structure for receiving andfixing optical fibers 106 that may be used at the sides 102 a and 102 binstead of the convergence block 152 and the optical fiber collimatorassemblies 134. In the structure depicted in FIG. 28a, a clamping plate602, micromachined from silicon, secures the optical fibers 106. Anadjustment plate 604, also micromachined from silicon, permits adjustingthe ends 104 of the optical fibers 106 that protrude therethrough bothfrom side-to-side and up-and-down, and then fixing the ends 104 in theiradjusted position. The clamping plate 602 is pierced by an array ofholes 606 which are etched through a 1.0 to 2.0 mm thick siliconsubstrate using the Bosch deep RIE process. The holes 606, which have adiameter only a few microns larger than the optical fibers 106,typically have a diameter of 100 to 125 microns which matches the outerdiameter of typical optical fibers 106. If the clamping plate 602 mustbe thicker than 1.0 to 2.0 mm, then two or more plates can be juxtaposedand registered kinematically to each other using V-groves and rods.After being registered, two or more juxtaposed clamping plates 602 canbe glued together.

The hole 606 positions the optical fibers 106 precisely with respect toeach other within a few microns. The high depth-to-diameter ratio of theholes 606, e.g. 10:1 or greater, facilitates fixing the optical fibers106 longitudinally. To ease insertion of optical fibers 106 into theholes 606, a pyramidally shaped entrance 608 to the holes 606, only oneof which is illustrated in FIG. 28a, may be formed on one side of theclamping plate 602 using anisotropic etching.

While the holes 606 may be formed as right circular cylinders, they mayalso have more complicated cylindrical profiles such as that illustratedin FIG. 28b. The holes 606 may be RIE or wet etched to provide a profilein which a cantilever 612 projects into the hole 606. The cantilever 612is positioned with respect to the remainder of the hole 606 so thatinsertion of the optical fiber 106 thereinto bends the cantilever 612slightly. In this way the cantilever 612 holds the optical fiber 106firmly against the wall of the hole 606 while permitting the opticalfiber 106 to slide along the length of the hole 606. The holes 606 mayincorporate other more complicated structures for fixing the opticalfiber 106 with respect to the holes 606. For example, a portion of eachhole 606 may be formed with the profile depicted in FIG. 28b while theremainder, etched in registration from the opposite side of the clampingplate 602, may be shaped as a right circular cylinder.

After the clamping plate 602 has been fabricated, optical fibers 106 areinserted through all the holes 606 until all the optical fibers 106protrude equally a few millimeters, e.g. 0.5 to 3.0 mm, out of theclamping plate 602. Protrusion of the optical fibers 106 this far beyondthe clamping plate 602 permits easily bending them. Identical protrusionof all the optical fibers 106 may be ensured during assembly by pressingthe ends 104 of the optical fibers 106 against a stop. The opticalfibers 106 may be fixed to the clamping plate 602 by gluing, soldering,or simply be held by frictional engagement with the cantilever 612.

The adjustment plate 604, best illustrated in FIG. 28c, includes anarray of XY micro-stage stages 622 also etched through a 1.0 to 2.0 mmthick silicon substrate using the Bosch deep RIE process. Each XYmicro-stage 622 includes a hole 624 adapted to receive the end 104 ofthe optical fiber 106 that projects through the clamping plate 602. Thedistances between holes 624 piercing the adjustment plate 604 areidentical to those which pierce the clamping plate 602, and may beformed with the profile depicted in FIG. 28b. Each optical fiber 106fits snugly within the hole 624.

FIG. 29 a depicts in greater detail one of the XY micro-stage stages 622included in the adjustment plate 604. An analogous monolithic silicon XYstage is described in U.S. Pat. No. 5,861,549 (“the '549 patent”) thatissued Jan. 19, 1999. FIG. 29a illustrates that the entire XYmicro-stage 622 is formed monolithically from a silicon substrate usingRIE etching. An outer base 632, that encircles the XY micro-stage 622,is coupled to an intermediate Y-axis stage 634 by four (4) flexures 636of a type described by Teague, et al. in, Rev. SCI. Instrum., 59, pg.67, 1988. Four similar flexures 642 couple the Y-axis stage 634 to aX-axis stage 644. The flexures 636 and 642 are of the paraflex type andtherefore stretch adequately for the XY motion envisioned for the hole624. The XY micro-stage 622 need only to be able to move and positionthe ends 104 of the optical fibers 106 over small distances which avoidsundue stress on the flexures 636 and 642. Other configurations for theflexures 636 and 642, similar to those described in the '549 patent, mayalso be used.

The XY micro-stage 622 likely omits any actuators, but the Y-axis stage634 may be fixed in relation to the outer base 632 with a metal ribbon,e.g. gold, kovar, tungsten, molybdenum, aluminum, or wire linkage 652.Similarly, the X-axis stage 644 may be fixed in relation to the Y-axisstage 634 also with a metal ribbon or wire linkage 654. The materialchosen for the linkages 652 and 654 preferably has a coefficient ofexpansion the same as or close to that of silicon. However, if thelinkages 652 and 654 are short, e.g. 100 microns, then even for a 20 PPMdifferential coefficient of expansion between the silicon and the metal(e.g. aluminum), the movement of the X-axis stage 644 with respect tothe outer base 632 would only be approximately 20 A° per degree Celsius.Metals other than aluminum provide even greater thermal stability.

In adjusting the XY micro-stage 622, the linkages 652 and 654 are firstbonded respectively to the Y-axis stage 634 and to the X-axis stage 644.By pulling the metal linkages 652 and 654 simultaneously while viewingthe end 104 of the optical fiber 106 through a microscope, the X-axisstage 644 may be moved along both the X and Y axes to position the end104 at a specified location. After the X-axis stage 644 has been move toproperly position the end 104, the linkages 652 and 654 are bonded orspotwelded in place.

The XY micro-stage 622 may include a lever 622 illustrated in FIG. 29cto reduce movement of the X-axis stage 644 in comparison with movementof a distal end 664 of the XY micro-stage 622. For the XY micro-stage622 illustrated in that FIG., etching to form the stages 634 and 644also yields the lever 622 that is cantilevered from the Y-axis stage634. The linkage 654 is initially bonded both to the X-axis stage 644and to the lever 622. A similar linkage 666 is fastened to the end ofthe lever 622 distal from its juncture with the Y-axis stage 634. Afterthe X-axis stage 644 has been move to properly position the end 104, asbefore the linkage 666 is bonded or spotwelded to the Y-axis stage 634.Alternatively, as illustrated in FIG. 29c, the linkage 654 may beomitted from the XY micro-stage 622 to be replaced by a flexible pushpin672, well known in the art, that couples between the X-axis stage 644and the lever 622 cantilevered from the Y-axis stage 634. Opposite endsof the flexible pushpin 672 are coupled by flexures 674 respectively tothe X-axis stage 644 and to the lever 622. The embodiment of the XYmicro-stage 622 depicted in FIG. 29c requires only one linkage 666 forfixing the X-axis stage 644 when the end 104 of the optical fiber 106 isat its specified location. Furthermore, the movement of the X-axis stage644 is now bi-directional because the flexible pushpin 672 can both pushand pull on the X-axis stage 644.

While the preceding description of the lever 622 has addressed onlyX-axis motion of the X-axis stage 644, it is readily apparent that asimilar lever could be incorporated into the outer base 632 foreffecting Y-axis motion of the Y-axis stage 634 and of the X-axis stage644 with respect to the outer base 632.

As described above, the XY micro-stage 622 permits fixing and adjustingthe ends 104 of optical fibers 106 along their X and Y axes. However,properly focusing the lens 112 with respect to the ends 104 of opticalfibers 106 may require relative movement either of the end 104 or thelens 112 along the longitudinal axis 144. The separation between the end104 of optical fiber 106 and the lens 112 may be adjusted in variousdifferent ways. Bright, et al., SPIE Proc., vol. 2687, pg.34, describe apoly-silicon mirror, moving like a piston, which may beelectrostatically displaced perpendicular to the substrate upon which ithas been fabricated.

FIG. 30a depicts a monolithic plano-convex lens 112 micromachined from aSOI wafer 162 using RIE etching that can be electrostatically displacedalong the longitudinal axis 144 perpendicular to the substrate uponwhich it was been fabricated. To permit electrostatically displacing thelens 112 along the longitudinal axis 144, as illustrated in FIG. 30b thelens 112 is supported from the surrounding device silicon layer 166 ofthe wafer 162 by three (3) V-shaped flexures 682. One end of theflexures 682, each of which extends part way around the periphery of thelens 112, is coupled to the surrounding device silicon layer 166 whilethe other end is coupled to the lens 112. Except for deflectionelectrodes 684 that are disposed to the right of the lens 112 in FIG.30a and electrically insulated from the wafer 162, the entire assemblyis made as one monolithic silicon structure. Electrostatic attractionbetween the electrodes 684 and the combined flexures 682 and the lens112, created by applying an electrical potential between the electrodes684 and the device silicon layer 166, pulls the lens 112 toward theelectrodes 684 along the longitudinal axis 144.

Silicon lenses suitable for IR optical fiber transmission arecommercially available and may be adapted for use in this invention.Accordingly, small individual commercially available micro-lenses may beplaced into a cavity etched into a flat membrane supported by theflexures 682. Alternatively, the lens 112 may be formed using RIE whilethe flexures 682 are being formed. Yet another alternative is to firstdiamond turn the lens 112 and then protect it from etching while theflexures 682 are formed using RIE. Still another alternative is to firstform the flexures 682 using RIE while protecting the area where the lens112 is to be formed, and then diamond turning the lens 112. After thelens 112 and the flexures 682 have been formed in any of these ways, thewafer 162 underlying them is removed with anisotropic etching to exposethe silicon dioxide layer 164. The backside 170 of the lens 112fabricated in this way is optically flat.

Instead of electrostatic actuation, the lens 112 may be moved along thelongitudinal axis 144 electro-magnetically. As illustrated in FIG. 30c,the electrodes 684 disposed adjacent to the lens 112 in the illustrationof FIG. 30a are replaced with permanent magnets 692 oriented with theirmagnetic field parallel to the longitudinal axis 144 of the lens 112.Also a coil 694 encircles the lens 112. Electrical leads from the coil694 are brought out to the device silicon layer 166, preferablysymmetrically, via the flexures 682 to ensure linear displacement of thelens 112. Depending upon the direction of current flow applied to thecoil 694, the lens 112 moves toward or away from the end 104 of theoptical fiber 106.

In a similar way, magnetic force, rather than electrostatic force, maybe used to effect rotation of plates 184 of torsional scanners 172 atleast about an axis of rotation established preferably by the torsionalflexure hinges 176, or by the torsion-bar hinges 182. FIGS. 31a and 31 bdepicts several magnets 696 all oriented in the same direction along astrip of torsional scanners 172. Thus, the individual magnetic fields,indicated by arrows 697, are all oriented in the same direction, andreinforce each other. The torsional scanners 172 also include coils 698disposed on the inner moving frame 178 thereof through which an electriccurrent flows when effecting rotation of the plate 184. Using such aconfiguration for the torsional scanners 172 permits removing from thesubstrate 212 the electrodes 214 that are juxtaposed with the innermoving frame 178. Typically, when the magnets 696 and coils 698 arepresent the substrate 212 will include cavities adjacent to the innermoving frame 178, as described in U.S. Pat. No. 6,044,705 that issuedApr. 4, 2000. Such cavities permit large rotations of the inner movingframe 178 about the axis established by the torsional flexure hinges176. As illustrated in FIG. 31b, the magnets 696 typically have atrapezoidal cross-section which allows the beam of light 108 to impingeupon the mirror surface 116 at a large angle. Alternatively, asillustrated in FIGS. 31c and 31 d the magnets 696 may be arrangedlinearly along opposite sides of the torsional scanners 172. Thisconfiguration for the torsional scanners 172 and the magnets 696provides better demagnetization factor for the magnets and strongerfields.

In many telecommunication applications for the fiber optic switch 400,light arriving at the fiber optic switch 400 may have previously passedthrough a routing wavelength demultiplexer which may typically be inintegrated chip form. A significant cost in fabricating routingwavelength demultiplexers is often that of connecting from its planarcircuit to outgoing optical fibers. If the reflective switching module100 of the fiber optic switch 400 described above is properlyconfigured, making connections between the routing wavelengthdemultiplexer and optical fibers becomes unnecessary. Rather, outgoingbeams of light from the routing wavelength demultiplexer are simplycoupled in free space to the lenses 112 of the reflective switchingmodule 100 which may include an anti reflection overcoating to reducereflection.

FIG. 32 illustrates an arrangement in which a routing wavelengthdemultiplexer 702 includes several demultiplexed planar waveguides 704.The demultiplexed planar waveguides 704 radiate beams of light 108directly toward the lenses 112 facing them thereby avoiding anynecessity for coupling the routing wavelength demultiplexer 702 tooptical fibers. A substrate 706 of the routing wavelength demultiplexer702, which carries demultiplexed planar waveguides 704, may be placedadjacent to the lenses 112 to supply incoming beams of light 108 to thereflective switching module 100. Likewise where outgoing beams of light108 leave the reflective switching module 100, the lenses 112 may couplethe beams of light 108 directly to demultiplexed planar waveguides 704from which the beams of light may be multiplexed into one or severaloutgoing optical fibers. By providing and reserving some extra outputand input holes 154 in the convergence blocks 152 for use withwavelength converters, the fiber optic switch 400 may provide wavelengthconversion for light received from any optical fiber coupled to thefiber optic switch 400.

Wavelength conversion is desirable in many applications for the fiberoptic switch 400. Wavelength conversion may be readily achieved byforming a grating 712 on the plate 184 of a torsional scanner 172 asillustrated in FIGS. 33a and 33 b. A laser diode 714 together with alens 716 and the grating 712 form a Littrow cavity similar to thosedescribed in U.S. Pat. Nos. 5,026,131, 5,278,687 and 5,771,252. In theLittrow cavity, the grating 712 carried on the rotatable plate 184reflects the first order diffracted beam back to the laser diode 714thereby establishing, with a rear facet of the laser diode 714, anoptical cavity for lasing. A beam splitter 722 directs a zeroth orderdiffracted output beam 724 to a wavelength locker 726 as is well knownin the art. Hence, rotation of the plate 184 carrying the grating 712varies the wavelength of light in the output beam 724. Feedback from thewavelength locker 726 may be used to control rotation of the plate 184thereby selecting a specific wavelength for the output beam 724.

FIG. 33b illustrates using the Littrow cavity in converting light in anincoming beam 732 to an arbitrarily selected wavelength. The incomingbeam 732 impinges upon a gain medium 734 that is excited by the laserdiode 714 to a level just below a threshold for lasing. The incomingbeam 732 at a first wavelength raises the gain medium 734 above thethreshold for lasing thereby causing lasing at a wavelength selected bythe orientation of the plate 184 that carries the grating 712. Again thewavelength locker 726 provides feedback for selecting a specificwavelength for the output beam 724.

In the illustration of FIG. 34, the structure of the grating 712 carriedon the plate 184 is used for measuring wavelength of light propagatingalong the optical fiber 106. Light extracted from the optical fiber 106by the directional coupler 424, or by the bent-fiber tap 495, passesthrough a lens 742 to impinge upon the grating 712. Diffracted lightfrom the grating 712, e.g. first order diffracted light, impinges upon alight detector 744 which may include a small collimating lens. Rotationof the grating 712 together with concurrently monitoring both an outputsignal produced by the light detector 744 and the signal produced by thetorsion sensors 192 included in the torsional scanner 172, whichmeasures the angular position of the grating 712, produces a spectrum ofthe light propagating along the optical fiber 106. The light detector744 may be physically very small and therefore quite inexpensive. Incomparison, diode arrays that respond well to infrared radiation arecomparatively expensive.

Although the present invention has been described in terms of thepresently preferred embodiment, it is to be understood that suchdisclosure is purely illustrative and is not to be interpreted aslimiting. Consequently, without departing from the spirit and scope ofthe invention, various alterations, modifications, and/or alternativeapplications of the invention will, no doubt, be suggested to thoseskilled in the art after having read the preceding disclosure.Accordingly, it is intended that the following claims be interpreted asencompassing all alterations, modifications, or alternative applicationsas fall within the true spirit and scope of the invention.

What is claimed is:
 1. A fiber optic switching module comprising: a) afirst and a second group of collimator receptacles which are separatedfrom each other at opposite ends of a free space optical path, and eachof which collimator receptacles is respectively adapted for receivingand fixing an optical fiber collimator assembly: that in turn receivesand fixes an end of an optical fiber, and which is adapted for emittinga quasi-collimated beam of light into the optical path; b) a first and asecond set of reflective light beam deflectors that are disposed in aV-shaped arrangement within the optical path between the groups ofcollimator receptacles, each of the light beam deflectors being:associated with one of the optical fiber collimator assembliesreceivable in the collimator receptacles; located so thequasi-collimated beam of light emittable from the associated opticalfiber collimator assembly impinges upon the light beam deflector to bereflected therefrom; and energizable by drive signals supplied to saidfiber optic switching module to be oriented for reflecting thequasi-collimated beam of light emittable from the associated opticalfiber collimator assembly to also reflect off a selected light beamdeflector; and c) a mirror disposed along the optical path between saidsets of light beam deflectors upon which quasi-collimated beams of lightimpinge; whereby a pair of light beam deflectors when selected andoriented by the drive signals supplied thereto, establish an opticalcoupling for at least one quasi-collimated beam of light between a pairof optical fiber collimator assemblies one of which is fixable in anyone of said collimator receptacles and another optical fiber collimatorassembly fixable in any other of said collimator receptacles.
 2. Thefiber optic switching module of claim 1 wherein the first group includesonly one collimator receptacle and the second group includes theremaining collimator receptacles whereby the fiber optic switchingmodule establishes the optical coupling between one optical fibercollimator assembly fixable in the single collimator receptacle and aselected one of the optical fiber collimator assemblies fixable in thesecond group of collimator receptacles.
 3. The fiber optic switchingmodule of claim 1 wherein individual collimator receptacles areconically-shaped and are adapted to receive a mating, conically-shapedoptical fiber collimator assembly.
 4. The fiber optic switching moduleof claim 1 further comprising environmental housing that encloses theoptical path through which the beams of light propagate.
 5. The fiberoptic switching module of claim 4 wherein the environmental housingprovides temperature regulation for maintaining a stable operatingenvironment for the fiber optic switching module.
 6. The fiber opticswitching module of claim 4 wherein dry gas flows through theenvironmental housing to hinder moisture from condensing within thefiber optic switching module.
 7. The fiber optic switching module ofclaim 4 wherein the environmental housing is pressurized to excludeatmosphere surrounding the environmental housing from entering the fiberoptic switching module.
 8. The fiber optic switching module of claim 4wherein the environmental housing includes a nonsaturable microdryer tohinder moisture from condensing within the fiber optic switching module.9. The fiber optic switching module of claim 4 wherein a wall of theenvironmental housing is pierced by an electrical feed-through throughwhich the drive signals pass.
 10. The fiber optic switching module ofclaim 1 wherein, when light beam deflectors are un-energized, beams oflight reflecting therefrom substantially converge in one dimension(“1D”).
 11. The fiber optic switching module of claim 1 wherein, whenlight beam deflectors are un-energized, beams of light reflectingtherefrom substantially converge in two dimensions (“2D”).
 12. The fiberoptic switching module of claim 11 wherein orientation of saidcollimator receptacles effects convergence of beams of light in a firstdimension, and orientation of said light beam deflectors whenun-energized effects convergence in a second dimension.
 13. The fiberoptic switching module of claim 1 wherein, when light beam deflectors ofthe first or of the second set are un-energized, the beams of lightreflecting therefrom substantially converge at a point that is locatedbehind a juncture of said sets of light beam deflectors.
 14. The fiberoptic switching module of claim 1 wherein, when light beam deflectors ofthe first or of the second set are un-energized, the beams of lightreflecting therefrom substantially converge at a point that is locatedat a juncture of said sets of light beam deflectors.
 15. The fiber opticswitching module of claim 1 wherein light beam deflectors of the firstor of the second set that require the greatest movement in reflecting abeam of light to any of the light beam deflectors in the second or inthe first set exhibit substantially equal clockwise andcounter-clockwise rotation angles from an un-energized orientation ofsuch light beam deflectors.
 16. The fiber optic switching module ofclaim 1 wherein light beam deflectors of the first or of the second setthat require the greatest movement in reflecting a beam of light to anyof the light beam deflectors in the second or in the first set: rotateabout two non-parallel axes: and exhibit substantially equal clockwiseand counter-clockwise rotation angles about at least one of the axesfrom an un-energized orientation of such light beam deflectors.
 17. Thefiber optic switching module of claim 1 wherein light beam deflectors ofthe first or of the second set that require the greatest movement inreflecting a beam of light to any of the light beam deflectors in thesecond or in the first set exhibit substantially equal bi-polar rotationangles from an un-energized orientation of such light beam deflectors.18. The fiber optic switching module of claim 1 wherein light beamdeflectors of the first or of the second set that require the greatestmovement in reflecting a beam of light to any of the light beamdeflectors in the second or in the first set: rotate about twonon-parallel axes: and exhibit substantially equal bi-polar rotationangles about at least one of the axes from an un-energized orientationof such light beam deflectors.
 19. The fiber optic switching module ofclaim 1 wherein light beam deflectors of the first or of the second setthat require the greatest movement in reflecting a beam of light to anyof the light beam deflectors in the second or in the first set exhibitminimum rotation angles from an un-energized orientation of such lightbeam deflectors.
 20. The fiber optic switching module of claim 1 whereinorientation of only the collimator receptacles effects convergence ofbeams of light.
 21. The fiber optic switching module of claim 1 whereinorientation of only said light beam deflectors when un-energized effectsconvergence of beams of light.
 22. The fiber optic switching module ofclaim 1 wherein drive signals supplied to the fiber optic switchingmodule for energizing orientation of each light beam deflector respondto a signal produced by an orientation sensor that is coupled to thelight beam deflector.
 23. The fiber optic switching module of claim 1wherein drive signals supplied to the fiber optic switching module forenergizing orientation of each light beam deflector respond to a signalproduced by an orientation sensor that is independent of the beam oflight reflectable therefrom.
 24. The fiber optic switching module ofclaim 1 wherein said light beam deflectors are respectively supportedfrom a frame by torsional hinges, and each frame, torsional hinges andlight beam deflector are fabricated from single crystal silicon.
 25. Afiber optic switching module comprising: a first and a second group ofoptical fiber receptacles, said groups of optical fiber receptaclesbeing separated from each other at opposite ends of a free space opticalpath, and each optical fiber receptacle being adapted for receiving andfixing an end of an optical fiber; lenses one of which is fixedrespectively at each of the optical fiber receptacles of the first andsecond groups so the end of the optical fiber fixable in that opticalfiber receptacle is juxtaposed with said lens fixed thereat, each saidlens being adapted for receiving a beam of light emittable from thejuxtaposed end of the optical fiber and for emitting a quasi-collimatedbeam of light into the optical path of the fiber optic switching module;c) a first and a second set of reflective light beam deflectors that aredisposed in a V-shaped arrangement within the optical path between thegroups of optical fiber receptacles, each of the light beam deflectorsrespectively being: associated with one of said lenses fixed at each ofthe optical fiber receptacles; located so the quasi-collimated beam oflight emittable from said associated lens impinges upon the light beamdeflector to be reflected therefrom; and energizable by drive signalssupplied to said fiber optic switching module to be oriented forreflecting the quasi-collimated beam of light emittable from saidassociated lens to also reflect off a selected light beam deflector; andd) a mirror disposed along the optical path between said sets of lightbeam deflectors upon which quasi-collimated beams of light impinge;whereby a pair of light beam deflectors when selected and oriented bythe drive signals supplied thereto, establish an optical coupling for atleast one quasi-collimated beam of light between a pair of lensesrespectively fixable at any one of said optical fiber receptacles andanother lens fixable at any other of the optical fiber receptacles. 26.The fiber optic switching module of claim 25 wherein the first groupincludes only one optical fiber receptacle and the second group includesthe remaining optical fiber receptacles whereby the fiber opticswitching module establishes the optical coupling between one lens fixedat the single optical fiber receptacle and one of said lenses fixed atthe second group of optical fiber receptacles.
 27. The fiber opticswitching module of claim 25 further comprising environmental housingthat encloses the optical path through which the beams of lightpropagate.
 28. The fiber optic switching module of claim 27 wherein theenvironmental housing provides temperature regulation for maintaining astable operating environment for the fiber optic switching module. 29.The fiber optic switching module of claim 27 wherein dry gas flowsthrough the environmental housing to hinder moisture from condensingwithin the fiber optic switching module.
 30. The fiber optic switchingmodule of claim 27 wherein the environmental housing is pressurized toexclude atmosphere surrounding the environmental housing from enteringthe fiber optic switching module.
 31. The fiber optic switching moduleof claim 27 wherein the environmental housing includes a nonsaturablemicrodryer to hinder moisture from condensing within the fiber opticswitching module.
 32. The fiber optic switching module of claim 27wherein a wall of the environmental housing is pierced by an electricalfeed-through through which the drive signals pass.
 33. The fiber opticswitching module of claim 25 wherein, when light beam deflectors areun-energized, beams of light reflecting therefrom substantially convergein 1D.
 34. The fiber optic switching module of claim 25 wherein, whenlight beam deflectors are un-energized, beams of light reflectingtherefrom substantially converge in 2D.
 35. The fiber optic switchingmodule of claim 34 wherein orientation of said optical fiber receptaclesand said lenses effects convergence of beams of light in a firstdimension, and orientation of said light beam deflectors whenun-energized effects convergence in a second dimension.
 36. The fiberoptic switching module of claim 25 wherein, when light beam deflectorsof the first or of the second set are un-energized, the beams of lightreflecting therefrom substantially converge at a point that is locatedbehind a juncture of said sets of light beam deflectors.
 37. The fiberoptic switching module of claim 25 wherein, when light beam deflectorsof the first or of the second set are un-energized, the beams of lightreflecting therefrom substantially converge at a point that is locatedat a juncture of said sets of light beam deflectors.
 38. The fiber opticswitching module of claim 25 wherein light beam deflectors of the firstor of the second set that require the greatest movement in reflecting abeam of light to any of the light beam deflectors in the second or inthe first set exhibit substantially equal clockwise andcounter-clockwise rotation angles from an un-energized orientation ofsuch light beam deflectors.
 39. The fiber optic switching module ofclaim 25 wherein light beam deflectors of the first or of the second setthat require the greatest movement in reflecting a beam of light to anyof the light beam deflectors in the second or in the first set: rotateabout two non-parallel axes; and exhibit substantially equal clockwiseand counter-clockwise rotation angles about at least one of the axesfrom an un-energized orientation of such light beam deflectors.
 40. Thefiber optic switching module of claim 25 wherein light beam deflectorsof the first or of the second set that require the greatest movement inreflecting a beam of light to any of the light beam deflectors in thesecond or in the first set exhibit substantially equal bi-polar rotationangles from an un-energized orientation of such light beam deflectors.41. The fiber optic switching module of claim 25 wherein light beamdeflectors of the first or of the second set that require the greatestmovement in reflecting a beam of light to any of the light beamdeflectors in the second or in the first set: rotate about twonon-parallel axes; and exhibit substantially equal bi-polar rotationangles about at least one of the axes from an un-energized orientationof such light beam deflectors.
 42. The fiber optic switching module ofclaim 25 wherein light beam deflectors of the first or of the second setthat require the greatest movement in reflecting a beam of light to anyof the light beam deflectors in the second or in the first set exhibitminimum rotation angles from an un-energized orientation of such lightbeam deflectors.
 43. The fiber optic switching module of claim 25wherein orientation of only said optical fiber receptacles and saidlenses effects convergence of beams of light.
 44. The fiber opticswitching module of claim 25 wherein orientation of only said light beamdeflectors when un-energized effects convergence of beams of light. 45.The fiber optic switching module of claim 25 wherein drive signalssupplied to the fiber optic switching module for energizing orientationof each light beam deflector respond to a signal produced by anorientation sensor that is coupled to the light beam deflector.
 46. Thefiber optic switching module of claim 25 wherein drive signals suppliedto the fiber optic switching module for energizing orientation of eachlight beam deflector respond to a signal produced by an orientationsensor that is independent of the beam of light reflectable therefrom.47. The fiber optic switching module of claim 25 wherein said light beamdeflectors are respectively supported from a frame by torsional hinges,and each frame, torsional hinges and light beam deflector are fabricatedfrom single crystal silicon.
 48. The fiber optic switching module ofclaim 25 wherein ends of optical fibers receivable into optical fiberreceptacles emit a beam of light at an angle with respect to a centerline of the optical fiber, and first faces of lenses respectivelyassociated therewith are oriented at an oblique angle with respect to alongitudinal axis of the lens so that within each lens the beam of lightis substantially aligned with the longitudinal axis of the lens.
 49. Thefiber optic switching module of claim 48 herein each lens has a focalpoint located substantially at the obliquely angled face thereof, andthe end of the optical fiber receivable into the optical fiberreceptacle associated therewith is positioned one Raleigh range of thebeam of light from the obliquely angled face.
 50. The fiber opticswitching module of claim 48 wherein optical fibers receivable intooptical fiber receptacles are duplex optical fibers and lensesrespectively associated therewith further have a second face that: isoriented at an oblique angle with respect to the longitudinal axis ofeach lens; and intersects with and is not parallel to the first facethereof, so that within each lens two beams of light, respectivelyexiting or entering the end of the duplex optical fiber respectivelyassociated therewith at differing angles with respect to the center lineof the optical fiber, are substantially aligned with the longitudinalaxis of the lens.
 51. The fiber optic switching module of claim 50wherein two beams of light propagate through the duplex optical fiber inopposite directions.
 52. The fiber optic switching module of claim 50wherein two beams of light propagate through the duplex optical fiber ina single direction.
 53. The fiber optic switching module of claim 25wherein lenses included in the fiber optic switching module arerespectively formed with a smaller diameter outer surface which isdisposed nearer to the end of said optical fiber receivable into theoptical fiber receptacle associated therewith, the lenses also beingformed with a larger diameter outer surface which is disposed furtherfrom the end of said optical fiber receivable into the optical fiberreceptacle associated therewith than the smaller diameter outer surfaceof the lens.